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Running Crossfire/SLI in x16/x4 mode?

hdpcgamer

hdpcgamer

hdpcgamer

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Joined
21 Dec 2010
Posts
1,213
Hi guys,

I'm planning on upgrading my bedroom gaming rig later this year and will end up buying either an AM3 motherboard, or a 1156 motherboard due to being on a tight budget and the GPUs I am likely going to buy is the either GTX 460 1gb or the HD 5850 1gb if its still available.

Ideally I'd like to buy a motherboard that will allow me to add an extra GPU later in the year or when I need the extra headroom and heres where I need advice on.

From my understanding and please correct me if I'm wrong, you can buy motherboards which offers and runs in the following dual GPU configurations (again I'm after purely a dual-GPU configuration):


1. x16/x4

2. x8/x8

3 x16/x16


Ok, here is where there seems to be a great deal of confusion as to how much of a performance hit you will get if you go from a configuration of x16/x16 to x16/x4.

The general consensus appears to be that unless you buy a motherboard which runs at either x16/x16 or x8/x8, its not worth adding a second card as the performance hit would be too much running in x16/x4.

However looking at the following articles appear to suggest otherwise.


http://www.techpowerup.com/reviews/AMD/HD_5870_PCI-Express_Scaling/25.html

http://www.hardocp.com/article/2010/08/25/gtx_480_sli_pcie_bandwidth_perf_x16x16_vs_x4x4


Does anyone have other benchmarks from reputable websites such a Tom's Hardware, Guru3D, AnandTech etc where they test each of those configurations (x16/x16 vs x8/x8 vs x16/x4)?

The reason why I ask is that there appears to be a noticable price difference between motherboards which support dual-GPUs and here are the price and configurations I have come up with:


x16/x4 Motherboads:

The cheapest AM3 motherboard I could find that starts at around £50 is the ASROCK M3A770DE 770 and for the 1156, it was the Asus P7P55 LX P55 at around £80.


x8/x8 Motherboads:

AM3 Motherboards which offer dual-GPUs at x8/x8 tend to be priced at over £100 which is a big increase in price but I did manage to find one for around £75 and that is the Asrock 870 Extreme3. For 1156 motherboards, the cheapest one I could find was the MSI P55A-G55 at around £90.


x16/x16 Motherboads:

We then move onto the higher-end motherboards that offer dual-GPU configuration at the maximum x16/x16, the cheapest AM3 one I could find, was the Asus M4A89TD PRO 890FX for around £130 and for 1156, the ASUS Maximus III Extreme at around a hefty £250.


If I decide to go the more affordable AM3 route then the cheapest dual-GPU configuration will cost me around £50 with the next up around £75 and then finally £130 for a motherboard that offers a full x16/x16.

Is it actually worth paying an extra £80 going from x16/x4 to x16/x16 for what appears to be just a 5% increase in performance?


If I choose the more expensive 1156 route, then the cheapest motherboard which runs at the lowest configuration would cost me £80 and paying just an extra £10 would fetch me a x8/x8 motherboard. However, the only socket 1156 motherboard I could find that runs in x16/x16 is the ASUS Maximus III Extreme at around a hefty £250.

I wouldn't even consider the ASUS Maximus III Extreme due to the price and how it is way too OTT for my needs but for £10 extra, the MSI P55A-G55 running at x8/x8 makes much more sense to me.


It would be great to hear everyones thoughts and experiences on running dual-GPUs at any of the above configurations and whether or not you think its worth the extra price premium going from a x16/x4 motherboard > x8/x8 > x16/x16 motherboard?
 
There is no point in asking now about motherboards, as later this year newer motherboards and cpu's will come out making it pointless asking about these boards as 1156 is eol and am3 is approaching eol.
 
of course there is a point, OP is on a budget therefore older tech = cheaper, and u do know it doesnt just stop working when something new comes out right :rolleyes:

As you can see from your articles 8x8x vs 16x16x produces very little difference so in your position I would save the money and get an 8x8x compatible board. U may find u never use the second PCIe slot and just run one gfx card in the first at 16x. Dont save too much if u do plan to xfire later tho as u need a motherboard that is capable to overclock the CPU u choose well otherwise the CPU will be the bottleneck in ur system.
 
Ask yourself, are you really going to go sli/cfx down the line?

I've encountered loads of builds where people have said that and just stuck with a single card and then upgraded to a newer single card and sold off the old one.

It will save you a fair few headaches right now and later on. Get the 460/1g or 5850 and later on sell it and move on. The cash saved not faffing about going after an sli/cfx motherboard you can put towards a better gpu now or later.
 
KiiYzOo said:
There is no point in asking now about motherboards, as later this year newer motherboards and cpu's will come out making it pointless asking about these boards as 1156 is eol and am3 is approaching eol.
Click to expand...

The thing is I am on a tight budget and it is highly unlikely that I will be able to afford a Sandybridge CPU/mobo or Bulldozer CPU/mobo and theres a good chance that once the dust settles on the new CPUs, the price for the current AM3 & 1156 will drop even further. Again, I am only looking at upgrading my bedroom rig to a mid-range gaming rig, not state-of-the-art.
 
creed said:
of course there is a point, OP is on a budget therefore older tech = cheaper, and u do know it doesnt just stop working when something new comes out right :rolleyes:

As you can see from your articles 8x8x vs 16x16x produces very little difference so in your position I would save the money and get an 8x8x compatible board. U may find u never use the second PCIe slot and just run one gfx card in the first at 16x. Dont save too much if u do plan to xfire later tho as u need a motherboard that is capable to overclock the CPU u choose well otherwise the CPU will be the bottleneck in ur system.
Click to expand...

It does look likely that I'll get an x8/x8 motherboard as that seems to be the best compromise for price vs performance.

Regarding the CPU bottleneck, am I correct in the the i5 760 CPUs have a higher chance of overclocking to 4ghz and over vs the X4 955, thus when I decide to go Crossfire/SLI, I won't encounter any bottleneck?
 
lay-z-boy said:
Ask yourself, are you really going to go sli/cfx down the line?

I've encountered loads of builds where people have said that and just stuck with a single card and then upgraded to a newer single card and sold off the old one.

It will save you a fair few headaches right now and later on. Get the 460/1g or 5850 and later on sell it and move on. The cash saved not faffing about going after an sli/cfx motherboard you can put towards a better gpu now or later.
Click to expand...

The thing is, I have always used a single GPU configuration in my builds and I have always wanted to try out Crossfire/SLI not just for the sake of it, but because it seems to work out being one of the cheaper options out there.

Say 1-2 years down the line the 460/5850 wasn't offering smooth playable framerates when I'm gaming at 1080p, I could grab a 2nd hand 460/5850 for around £50 (doubt they will still be selling 460/5850 new in 1-2 years) and get a performance boost of 1.8-1.9.

Is it likely that I'll get the same boost in performance from a single GPU for £100?
 
hdpcgamer said:
You mean use dual-GPUs in x8/x8?

But the drop in performance is only 2%. :confused:
Click to expand...

I'm currently running 2 6870's in an Asus P5Q deluxe that will only crossfire at x8 / x8 and my benchmark scores are no different from systems that crossfire at x16 / x16 - anybody that says otherwise is talking donkey fodder i'm afraid!
 
^Andy^ said:
I'm currently running 2 6870's in an Asus P5Q deluxe that will only crossfire at x8 / x8 and my benchmark scores are no different from systems that crossfire at x16 / x16 - anybody that says otherwise is talking donkey fodder i'm afraid!
Click to expand...

Thanks, thats the kind of answer I was hoping to hear and it does seem to comfirm the benchmards floating around regarding x8/x8 vs x16/x16.:)

As your system seems to be close to what I will be upgrading to, what CPU are you using and is it overclocked to remove any bottlenecks?
 
hdpcgamer said:
Thanks, thats the kind of answer I was hoping to hear and it does seem to comfirm the benchmards floating around regarding x8/x8 vs x16/x16.:)

As your system seems to be close to what I will be upgrading to, what CPU are you using and is it overclocked to remove any bottlenecks?
Click to expand...

I'm running a Q9550 overclocked to 4ghz with a corsair H50 to keep it cool. I honestly can't say that I've seen the CPU cause a bottleneck (thats not to say that it hasn't happened - just that I haven't noticed it).
 
^Andy^ said:
I'm running a Q9550 overclocked to 4ghz with a corsair H50 to keep it cool. I honestly can't say that I've seen the CPU cause a bottleneck (thats not to say that it hasn't happened - just that I haven't noticed it).
Click to expand...

Thanks.

Hopefully I'll also be able to overclock either the i5 760 or the X4 955 to 4ghz when I go Crossfire or SLI.
 
Has anyone done any tests with newer gfx cards (58xx or 6xxx) cards with a x16/x4 crossfire setup. On PCIe 2.0 the articles I've read showed a very negligable performance hit, but they are older articles not on these new cards.
 
kristmace said:
Has anyone done any tests with newer gfx cards (58xx or 6xxx) cards with a x16/x4 crossfire setup. On PCIe 2.0 the articles I've read showed a very negligable performance hit, but they are older articles not on these new cards.
Click to expand...

Is this question directly related to your current setup?

Although I haven't found any x16/x4 crossfire/SLI benchmarks, going purely by the techpowerup 5870 PCI-Express Scaling benchmark, if you decide to add another 5850 to your motherboard with your existing 5850 occupying the x16 PCI-E slot and the other using the x4 slot, you should only be losing around 5% vs a full x16/x16 configuration.
 
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Can't speak for the AMD chip, but my i5 750, (which is identical to the 760 bar the multiplier) hit 4GHz with ease. I'm going SLI today or tomorrow when my second GTX460 arrives. I'll let you know how it is at x8/x8 :D
 
Blue160 said:
Can't speak for the AMD chip, but my i5 750, (which is identical to the 760 bar the multiplier) hit 4GHz with ease. I'm going SLI today or tomorrow when my second GTX460 arrives. I'll let you know how it is at x8/x8 :D
Click to expand...

Would be great to see what kind of fps you get with Crysis maxed out as there are people out there who claim to be hitting 60fps on average.:eek:
 
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