The nVidia cards were tested on an Asus A8N32-SLI using an Athlon 64 FX-60, 2GB of CMX1024-3500LLPRO RAM and a Seagate Barracuda ST340083A8 hard disk. Power was supplied by a Tagan 900W TG900-U95. For ATI testing, everything was kept the same except for the use of an Asus A8R32-MVP Deluxe and an Etasis 850W ET850.
All of the nVidia cards were tested using the beta 91.29 ForceWare drivers. The 7900 GTs running in SLI at standard clock speeds were tested using the slightly older 84.17. The X1900 XTX were tested using the official Catalyst 6.5 drivers.
Using our proprietary automated benchmarking suite, aptly dubbed 'SpodeMark 3D', I ran Call of Duty 2, Counter Strike: Source, Quake 4, Battlefield 2 and 3DMark 06. Bar 3DMark06, these all run using our in-house pre-recorded timedemos in the most intense sections of each game I could find. Each setting is run three times and the average is taken, for reproducible and accurate results. I ran each game test at 1,280 x 1,024, 1,600 x 1,200, 1,920 x 1,440 and 2,048 x 1,536 each at 0x FSAA with trilinear filtering, 2x FSAA with 4x AF and 4x FSAA with 8x AF.
I was interested to see how using the PCI Express bridge affected performance, so I set two 7900 GTs to the same clock speeds as the 7950 GX2 and used the same 91.29 drivers for comparison. I also decided to test Call of Duty 2 with the SLI Optimisations turned both on and off, to see how much difference this made to the 7950 GX2 and the two 7900 GT cards, in an effort to prove that this is not just a single card.
Obviously there were a lot of results to look at, but the questions in my mind were: how does it compare to the X1900 XTX (currently the fastest single card available), how does it compare to a pair of equally clocked 7900 GTs, and how does it compare to a pair of similarly priced full-speed 7900 GTs.
I also managed to overclock this card to 600MHz on the core and 800MHz (1,600MHz effective) on the memory and these performance results are included for comparison.
Having the two GPUs on one card should fractionally improve performance over an SLI solution as there is less latency. This was in fact the case, with one or two frames per second being noticed, but certainly nothing major. In the higher resolutions however, these differences became quite large indeed – 38 fps compared to 30. That's quite a performance difference considering how little has changed. In Counter-Strike: Source, the difference was even larger, 60 fps versus 24. This was enough to make me wonder if something fishy was going on.
I went back in to the games and decided to look for myself, as my concern was that AA was not being switched on. I was wrong. However, the level I use in Counter-Strike: Source contains HDR effects and on the 7950 GX2 card I noticed a few errors in the console when loading HDR textures. I think there is a bug in the 91.29 drivers that is causing these high results. For the best indication of 7950 GX2 performance, I would sooner you take more notice of the downclocked 7900 GTs in SLI, than the 7950 GX2 results.
In most cases, the 7950 GX2 (or simulated 7950 GX2) was faster than two full-speed 7900 GTs. I think that's because in most cases the extra memory bandwidth isn't needed and the increased core speed helps things a long more. However, in the highest setting of Counter-Strike: Source, the memory bandwidth was obviously needed as it attained 35 fps instead of 24, and that's using older drivers too.
The final question, is how does this compare to the X1900 XTX? Feature wise, the X1900 XTX obviously has FSAA+HDR on its side. On the performance side however, the ball was clearly in nVidia's court with the 7950 GX2 being on average 30 per cent faster. However, the fact that nVidia needs a second GPU to attain this is testament to the technology behind the X1900 XTX.
The 7950 GX2 is the fastest card available for a single slot motherboard, full stop. However, calling it a single GPU is misleading and anyone considering purchasing one should be aware of its caveats – mainly that games requires an SLI profile and that it can't run dual monitors without tediously disabling "Dual GPU" mode.
At around the £400 mark, this is a lot to pay for a graphics card and unlike running SLI, which can be split up into two manageable chunks – this must be paid for all at once. I would only consider doing so if I didn't have an SLI motherboard, or had the full intention of upgrading to Quad SLI in the future. For most people, a single 7900 GT and then adding a second in six months time would offer better value for money.
All in all though, this is not the disappointment I thought it would be. It's fast, quiet and the price is competitive for the performance.