Any issues running SLI with one card at x16, one at x8 (PCIe 3)

[wunkley]

I'm going to build a new dedicated gaming rig from the ground up in 3 or so month's time. Main thing I'm umming and ahhhing over is to wait for Skylake, or go X99 hex core (I really like the idea of 6 physical cores over 4, as I think some games will start to benefit).

I'm posting this in the GPU section, as I have concerns about running 2 cards in SLI at differing PCIe speeds. Bear with me....

From my limited research, if I do go x99 I would most likely get a 5820k chip. This 'only' allows 28 PCIe 'lanes', so if you run 2 cards in SLI, one will be at x16 and the other at x8. This is as I understand it, is that right?

Now, I'm no expert, but I'm something of an obsessive about using SLI and experiencing and eliminating stutter and microstutter in certain games. I've used SLI for years, currently on 780Ti SLI. I want to go one TX probably to start with, but have itchings to try out 4k soon, so will end up needing 2 cards. It will happen

It may be daft, but I can just sense problems arising from running 2 cards in SLI at different PCIe speeds. So my questions are:

1. Does anyone run this 5820k x99 set up now with SLI and have any input?
2. Are there any motherboards that allow you to force x8 for both cards, rather than one at x16 and one at x8? From what I've read x8 with "PCIe 3" is more than good enough anyway.
3. Should I just fork out for a 5930k with the full 40 lanes so there are no issues and both cards will run at x16
4. Should I wait for and get Skylake instead?

Ta

 

[VincentHanna]

I run a 5930k with TitanX SLi @ PCIE 3.0x16

Can I limit one to PCIE 3.0x8 in the BIOS? or would I have to physically move it?

Just thought I could run a heaven 4.0 benchmark for comparison if it's easy. I'm not moving cards about though.

 

[wunkley]

I run a 5930k with TitanX SLi @ PCIE 3.0x16

Can I limit one to PCIE 3.0x8 in the BIOS? or would I have to physically move it?

Just thought I could run a heaven 4.0 benchmark for comparison if it's easy. I'm not moving cards about though.

You tell me bud

It's not so much slightly reduced performance I'm concerned about. I have no doubt it would be negligible anyway. It's the dreaded SLI MICROSTUTTER issues I'm bothered about. I just want to do everything possible to eliminate any possible SLI stutter issues for my new build. And I have this (maybe irrational) idea that running 2 cards at different PCIe speeds (like they will in an X99 5820k setup) might cause stutter probs...

 

[VincentHanna]

I get where you are coming from.

I guess you would need to monitor difference in frametimes.

DX12 could solve all that anyway though.

 

[Kaapstad]

Get a 5930k and then all options are open.

Having said that I don't notice any difference using a 5960X, PCI-E 3.0 and SLI X16/X8/X8/X8

 

[old gamer]

i have a 3770k and asus p8z77- v pro, 980 sli and both pci slots revert to 8x when used, ive not noticed any problems running this


just had the look at the heaven benchmarks and im still no 15 so it does not look to be holding me back

 

[varkanoid]

I thought if you had say a card in a x16 slot and one in a x8 slot then it would run x8/x8 automatically ?

 

[old gamer]

I thought if you had say a card in a x16 slot and one in a x8 slot then it would run x8/x8 automatically ?

this what mine does

 

[wunkley]

I thought if you had say a card in a x16 slot and one in a x8 slot then it would run x8/x8 automatically ?

So did I. But from what I've read, on X99 and using a 5820k CPU it will run one card at x16 and one at x8. What I'm trying to find out is what I posted in my opening post, and if this might cause any issues with STUTTER.

 

[Churchy89]

I'm running a 4930k with two GPUs in SLI and a third dedicated PhysX card. They run at x16(SLI) x8(SLI) x8(PhysX) and I've never had issues with micro stutter or anything else of that nature. Hope that helps!

 

[Gripen90]

So did I. But from what I've read, on X99 and using a 5820k CPU it will run one card at x16 and one at x8. What I'm trying to find out is what I posted in my opening post, and if this might cause any issues with STUTTER.

I have been running 3 way SLI with a Core i7 4930K, Asus P9X79 Pro and 3x GTX 970 - all running x16x8x8 due to mothboard not having PLX chip. I had that board since late 2011 and never had stuttering issues due to running those speeds.
Now I have MSI X99S SLi Krait Edition, Core i7 5820K and 3x GTX 970 and they are running x8x8x8 and still not a single stutter issue and also I haven't noticed any performance difference running x16x8x8 vs x8x8x8 at all !
Don't get a 5930K ! IMO a waste of money and the PCI-e lanes make squat difference. I would have liked a 5930K just for "epeen" purposes but as I now see that the difference between 5820K vs 5930K is virtually non-existant, I can't get myself into buying a 5930K not even later on... only a 5960X due to the 8 cores.

 

[Tetsujin]

So! I've just built a rig around an Asus X99-A, with a 5820k, and twin MSI 970s. First thing to note is no full screen benchmarks (Unigine Heaven, 3DMark) would even run at all to begin with, got driver crashes, until hours of trawling the net suggested changing the PCI-e slots to Gen2, at which point it worked*.

Now it's all sitting pretty though, no seeming troubles with the x16x8 side of things. Benchies are exactly as they should be, compared to other similar rigs.

*Which turned out to not be it. At the same time as changing the slots to Gen2 spec, I also re-seated the SLI bridge the other way up and on the other set of connectors. After an experiment last night where I set the PCI-e slots back to Auto, and saw that full screen benchies worked still, it turned out to be the SLI bridge playing up. Bizarre. Protip never change two things at once when trying to fix a thing!