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Which 280x to Crossfire with?

chivs688

chivs688

chivs688

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27 Nov 2010
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706
I currently have an Asus 7970 Matrix Platinum, and am looking to add in a 280x to Crossfire with it.

This will be my first dual GPU setup, so not entirely sure what I'm looking for in terms of ideal compatibility, especially as they won't be identical cards.

So any suggestions?
 
Does the memory clock matter? I presume it does. .

And in that case, seeing as my 7970 runs at 6600MHz, should I be getting say the Asus Radeon R9 280X DirectCUII TOP, which is the closest at 6400MHz? And the core clock is only just lower at 1070MHz to my 1100MHz, so should be easy to bump it up slightly to match.?
 
I've got a Gigabyte Z77-D3H Motherboard, and a Corsair 600T case.

I was having a look at the measurements last night, and my 7970 is pretty damn huge, so I'm thinking that'll have to go on the bottom in order to get decent air flow to the 2nd card, which all seem to be about half the height.
 
In that case, you may want to think about upgrading the mobo as it'll be running x16/x4 :(
This isn't the end of the world, however it'll be less than optimal - especially in conjunction with the 2500K. You'll still get a big performance boost, but you'll likely see lower usage on the 2nd card. Not sure about any other problems.
 
How much less performance would I be getting due to it being x4?

And when you say especially in conjunction with my 2500k, what do you mean by that?

Oh and this is typical seeing as I only fairly recently upgraded to this Mobo hah.
 
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ED: Then again...^

I dunno, 5-15% or something? Nothing too major.

I meant that with it being Sandybridge/PCIe 2.0. If it was Ivy/Haswell PCIe 3.0, it probably wouldn't be a problem at all.

Like I say, it's probably not that big a deal. I remember running 7970/7950 xfire with a 2500k on a 650w psu in BF3 for an hour or so and it was all cool :)
 
Hmm, and the annoying thing is I'll be buying a motherboard for my 2500k, which will be the next thing I'll want to upgrade, which means I'd then have to get another new motherboard that fits the new cpu model when I do..
 
Well after some more digging, it seems that the performance difference could well be very minimal.

Looking at this article for instance, it would seem that the performance difference between x16 and x4 is very small indeed, being about 1 or 2 FPS in most cases shown there.

But there I believe they are comparing it with just the single card in each slot. Would there be any reason for it to be more impactful in Crossfire?

Although that is done with Ivybridge, and you did mention that my Sandybridge CPU could have a bigger issue with it..
 
Ah right thanks.

So I'm thinking at the moment of maybe just giving it a shot with my current board and seeing what the results are. If it's performing significantly worse than what they should do on at x8/x8, then either I can grab the ASRock or just wait it out until I've got the money to upgrade my CPU and do it then.
 
Thanks for the help :)

So just the last thing if you don't mind, regarding which 280x to get (which was what this thread was going to be about anyway hah).

Seeing as my 7970 runs at 6600MHz, should I be getting say the Asus Radeon R9 280X DirectCUII TOP, which is the closest at 6400MHz? And the core clock is only just lower at 1070MHz to my 1100MHz, so should be easy to bump it up slightly to match.?

Any reason to get another card over this one?
 
Don't worry about them matching out of the box. You can just adjust the clocks of whichever card to match (not that they absolutely have to match).

The only real thing to be concerned about is airflow to each card given that your matrix is already exhausting into the case and takes up three slots.

Do you have/still have the side panel with 4 fan slots? If so, get at least a couple of 120mm fans on there set to exhaust directly to the side or just above the cards. Also, make sure the front intake is as unobstructed as possible.

If the DCUII is a bit fat, maybe check out the HIS IceQ x2 (turbo/non turbo) as that's nice and slim + the cooler is pretty good, if perhaps not quite as good as the DCUII.
 
My understanding was that the Asus was the thinner of the two. .

The dimensions here show the HIS as being 31.1 x 15.1 x 4.2 cm. And the Asus is shown here to be 11.2 " x 5.7 " x 1.5 " Inch (1.5 inches being 3.8cm).

Or am I messing something up here?
 
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It shouldn't be slimmer than the HIS.
It is slimmer than I thought though, as it turns out that that particular card is only a little over two slots deep, rather than the three slot version I took it for.

You should be fine either way in that case. Just keep an eye on temps and ventilation :)
 
Yeah I do still have the side metal cover which I could put on and add some fans to, so I'll definitely do that.

Tested the 7970 in the lower slot and it just about fits in there with a bit of room left underneath for air to get out of. Not ideal but should be ok. And then I can put the new card in the above slot so then at least that one will have plenty of breathing room.

Now just that final hurdle of parting with all that money...

Thanks for all your help :)
 
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