CrossfireX vs SLIQuad

[laywill]

As an overclocking junkie I would like to try and clear up an issue which has been bugging me for a while: in a 4 GPU arrangement, is it better to side with ATI or nVidia?

All of the top scores on hwbot.org (sorry cant post URLs yet, ) for 3DMark06 are achieved using 4 Radeon 4890 cards in CrossfireX combined with an overclocked Xeon W3540 or i7 975 CPU.

I can fuly understand the choice of CPUs - them both being the best performing CPUs around with at least 4 cores and huge overclocking potential. But the GPU choice confuses me because a Radeon 4890 is less powerful than a 285GTX (i.e. 1 half of a 295GTX). So when you combine 4 of each surely the CrossfireX 4890s have less total power than a pair of 295GTX cards?

If you are still with me, can you thus explain why the paired 295GTX cards are less powerful! Is it a case of the performance of the cards from nVidia scaling less well than those of ATi when combined in multi-card setups? (I have heard about nVidia performancedecreasing relatively as more cards are added in a setup, i.e.: 1X, 2X, 2.8X, 3.4X. But is the same scaling issue true for ATI based cards?)

If anybody is particularly keen to rectify my muddled mind, does somebody know if combining 2 ASUS MARS 295GTX would produce a significant performance boost over 2 standard 295GTX cards in SLI; and whether the ASUS combo would beat 4 4890 cards in CrossfireX?

I most heartily thank anybody who can clear this issue up for me! Although my piggy bank is not quite up to paying for any of the aforementioned setups to do a personal comparison, I would be grateful for the knowledge. Thanks again!

[Fuzzed_out]

From what I know, and I fully expect to be ripped to shreds

Tri-SLI is the max, though if its 2 dual gpu cards I really dont know what will happen

Due to scaling of both SLI and x-fire I doubt the difference would be hugely noticeable

[laywill]

Thanks Fuzz,
If you put 2 dual GPU cards together in SLI you get quad SLI.

Its the sort of notion that "I doubt the difference would be hugely noticable" which I would like to clear up, because there is a 3000 Mark gap in hwbot.org 's records for 3DMark06 between 2 295GTX cards in SLI and 4 4890 cards in x-fire.

[Fuzzed_out]

3000??? seriously?

I'm going to look that up, would never have expected it to be anywhere close to that much and it sounds a good read if there is an article to boot.

Sorry for the apparently extremely false information.

[laywill]

No problems,
It is this huge gap between the 38000 marks of the 4890s and the 35000 marks of the 295GTXs which has left me asking why so if the 4890 is the less powerful card!

[Fuzzed_out]

http://www.tomshardware.com/reviews/...-295,2123.html

Did you crossreference this article with another? or is there one with both the 4890 Quad-Fired and GTX295 SLI as this one only has a double helping of 4870x2 to compare nVidia's pair of monsters to, even so at high resolutions on crysis (2560*1600) I was surprised to see the 4870x2 crossfired beating the GTX295s with an underdog-stick into the ground

[sammorris]

Nobody seems to have noticed, a GTX295 is not two GTX285s, it is two GTX260s.

[Terbinator]

Nobody seems to have noticed, a GTX295 is not two GTX285s, it is two GTX260s.

But i thought it was 2 GTX 275's and becuase of this the reason everyone was fapping over them new Asus MARS cards was because they combined 2x GTX 285 rather than the reference 2x 275's.

Also, dont forget the memory speed those 4890's push and 3Dmark doesnt really show how they perform game wise.

[nightkhaos]

The problem I have noted with beyond SLI and Crossfire configurations that include in excess of 2 cards is that of yet, the balance is not very effective. With 2 cards the scaling is almost linear, but it gets progressively worse with the more cards you add.

[sammorris]

Nope, it's two 260s. If it were 275, the GTX295 would actually be worth its absurdly high asking price.
Nightkhaos: Recent drivers have changed that. There are quite a lot of games showing over 300% scaling for 4 GPUs.

[shaithis]

Including some rather large claims in the very latest ATI/AMD driver release notes.

[sammorris]

One of them at least (Crysis Warhead) is true. The performance difference there is vast.

[kalniel]

As an overclocking junkie I would like to try and clear up an issue which has been bugging me for a while: in a 4 GPU arrangement, is it better to side with ATI or nVidia?

All of the top scores on hwbot.org (sorry cant post URLs yet, ) for 3DMark06 are achieved using 4 Radeon 4890 cards in CrossfireX combined with an overclocked Xeon W3540 or i7 975 CPU.

Are you comparing scores with the same overclocked CPU? Multi-GPU setups are more or less entirely constrained by CPU above 3 GPUs. When that happens then additional cards actually reduce performance because of increased CPU overhead.

If you are still with me, can you thus explain why the paired 295GTX cards are less powerful!

If the CPUs are exactly the same yet 2x295 is slower then it's simply that the CPU overhead is more, and both are constrained by CPU.

If anybody is particularly keen to rectify my muddled mind, does somebody know if combining 2 ASUS MARS 295GTX would produce a significant performance boost over 2 standard 295GTX cards in SLI; and whether the ASUS combo would beat 4 4890 cards in CrossfireX?

No in both cases, due to the CPU limitations. Such limitations are being addressed as much as possible now, especially in conjunction with chipsets (AMD have started concentrating on whole system performance, so how to optimise communication between cards, chipset and CPU for example, which should show some benefits. However you can't seriously consider AMD systems at the very top level unfortunately due to the dominance of Intel high end CPUs).

[sammorris]

Depends on the 3dmark, 3dmark06 is an absolute CPU bottleneck at 1 GPU, but Vantage shows a reasonable improvement with multiple cards.
Four 4890s are actually a more powerful combination than two 295s, as you're basically comparing 4 GTX260s vs 4 HD4890s - and the HD4890 is a much more powerful GPU. In low-resolution environments where the GTX295's poor memory performance doesn't show up, it will beat two HD4870X2s because Quad SLI scaling is better, but not four HD4890s.

Two MARS cards would be better, since the GTX285 is more powerful than the HD4890 (though not by very much, considering this is £2050 vs £530, maybe 10-15% at most?). If you're going for quad crossfire, as said, AMD CPUs are slightly more optimised, but their lack of performance means at this level, Intel are your only option. The new driver performance updates apply to Intel as much as AMD from what I can see.

[kalniel]

Four 4890s are actually a more powerful combination than two 295s, as you're basically comparing 4 GTX260s vs 4 HD4890s - and the HD4890 is a much more powerful GPU.

The GPUs in the 295GTX have more shaders than the 260 - the same number as the the GTX275 in fact. Though it has a lower clockspeed than the latter.

But as I mentioned, talk of GPU power is meaningless when you're bottlenecked by the CPU/subsystem.

[sammorris]

You certainly are in 3dmark, but in real world applications, the CPU bottlenecks aren't always as apparent at high resolutions. Let's face it, to be considering quad SLI/CF, you should really be using 2560x1600, 1920x1200 perhaps, but dual graphics can deal with 1920 pretty well enough (especially two 4890s)