Some benchmarks of some latest DirectX games in Vista: http://www.tomshardware.co.uk/DirectX10-Geforce-Radeon,review-29666.html
In conclusion, most cards seem to struggle to come up with decent framerates, unless you spend a fortune on a GeForce 8800.
The Radeon HD2600 Pro/XT seem to be faster than the GeForce 8400 and 8500, but usually slower than the 8600.
They're using early samples of the Radeon cards for some unknown reason, and they won't even run BioShock without crashing, bizarrely.
The overall consensus is that DX10 seems to hurt performace with some of those benchmarks seeing cards barely reaching 1FPS!
In conclusion, most cards seem to struggle to come up with decent framerates, unless you spend a fortune on a GeForce 8800.
The Radeon HD2600 Pro/XT seem to be faster than the GeForce 8400 and 8500, but usually slower than the 8600.
They're using early samples of the Radeon cards for some unknown reason, and they won't even run BioShock without crashing, bizarrely.
The overall consensus is that DX10 seems to hurt performace with some of those benchmarks seeing cards barely reaching 1FPS!