ATI Catalyst 9.12 WHQL Released
 

To begin with, application-specific performance increments include an overall performance improvement as high as 9% on the ATI Radeon HD 5800 Series and ATI Radeon HD 5700 Series, for 3DMark Vantage. GT1 - Jane Nash performance improves as much as 15% and FT4 - GPU Cloth improves up to 15%. Performance improves as much as 6% on single card configurations for S.T.A.L.K.E.R. - Call of Pripyat. The release provides DirectCompute 10.1 support for ATI Radeon HD 4800 and HD 4700 GPUs in both single and multi-GPU configurations. Lastly, this release adds support for certain OpenGL 3.2 extensions for all GPUs from Radeon HD 2000 series and upward (HD 3000, HD 4000, and HD 5000).


http://www.techpowerup.com/110750/AT..._Released.html

So this driver improves benchmarking performance....

I must say that the latest Catalist drivers (both 9.11 and 9.12) work way better under Win7 than NVidia's Detonators do. I've replaced my Asus 8800GTS with a Sapphire 5770 in my 'old' system yesterday (the 5870 doesn't fit because of sitting in front of the mainboard's S-ATA connectors) and two things were immediately noticable: one, that Oblivion, Borderlands and The Saboteur games all of a sudden look awesome and don't stutter any longer, and two, the games don't crash no more (especially Oblivion was 'accident-prone' under the NVidia drivers).
On the graphic drivers front, both NVidia and ATI had some serious ups and downs in the past, with NVidia (hearsay, as I've never had an ATI card before) usually having the most stable ones. For now though, it seems ATI have the upper hand with their latest drivers. Especially when running Win7.

The original 8800GTS cards would have performance issues under those games at moderate to higher resolutions with full details, I would expect at minimum a small performance increase with that upgrade, larger depending on vRAM/settings used.

I haven't run ATI hardware in a good while, but I can say I've not had NVIDIA driver issues with my GTX 260 on Windows 7 64bit starting with the RC. The only driver issues I have with them are game specific regardless of OS.... really annoying they can never fix their own "meant to be played" games.