The X1900 XT-X ran perfectly without any issues, but both the GeForce 7950 GX2 and the new X1950 XT-X gave me some issues.
At first, the 7950 GX2 would not boot in the machine unless I put it in the x4 PCI-E slot. From there, I had to update the BIOS in order to get the board to support it. This is a known issue with GX2 boards, but this is the first time I've experienced it. After the update, it ran fine. However, you might notice that Prey performance is less than spectacular. This is because the used 91.31 drivers don't have an SLI profile for Prey. Although there is a beta driver available that adds such a profile on nZone.com, I don't like to use beta drivers unless I have to. We can take a pretty good guess at Prey performance by looking at Quake 4 figures, but this does illustrate a key problem with the 7950 GX2 – if there is no SLI profile, you'll get considerably lower performance.
The X1950 XT-X had problems of its own too. I would erratically get a solid screen of green. Our testing suite runs timdemos for quite a few hours and comes in and out of 2D/3D modes a lot. It seems the service that ATI uses for switching between 2D and 3D clocks was not happy with the speed at which we were doing this. I solved this by forcing the 3D clocks on as default and turning off the service. This is no the first time I've had issues like this, so I'm hoping ATI will take a look at the service.
So how was performance? The X1950 XT-X was generally 5-10 per cent faster than the X1900 XT-X. Ignorning the Prey results, which do little more than give an example of what happens when there isn't an SLI profile, the 7950 GX2 was consistently faster than the X1950 XT-X, sometimes by considerable amounts. In the lower resolutions, things often played in ATI's direction, but in the resolutions that matter and with FSAA and AF switched on, nVidia pulled away.
However, frame rates are not everything – we all know there is more to the story. Firstly, there is no denying that ATI's filtering methods give considerably better quality images than the competitors, and I'd sooner sacrifice a few frames per second for this. Secondly, ATI support full precision HDR and FSAA simultaneously , something nVidia hardware can't do. Granted, there are only three titles on the market that can take advantage of this (Oblivion, Black & White 2, Far Cry), but I'm sure this list will get longer.
ATI has announced X1950 XT-X CrossFire cards, which means there is an easy upgrade opportunity that should reap considerable benefits. Although you can now add a second 7950 GX2 in to a machine for Quad SLI, there are diminishing returns when scaling four GPUs.
Finally, there is price. Overclockers.co.uk has several cards at around the £330-350 mark including VAT. That's phenomenal for a top-end card. In comparison, the 7950 GX2 is around £360-380 including VAT.
It's almost silent, the drivers are better, has a better feature set, better price, better image quality and it's ready to be paired with a CrossFire edition card. The 7950 GX2 may be slightly faster and doesn't need a specific card to run in SLI, but if it was my choice, I know what I'd be taking home to meet the parents.