We know that ATI and Valve worked together on aspects of Half Life 2, but how deep really did the co-operation run? The answer is of little surprise, given that the first benchmarks were over one year ago, but now that the final game is released to retail, we can be absolutely and completely fair.
"NVIDIA's NV3x line of GPUs - they still must be treated as DirectX 8 hardware, otherwise they suffer extreme performance penalties when running Half Life 2 using the DirectX 9 codepath. To give you a little preview of what is to come, in DirectX 9 mode, the GeForce 5900 Ultra offers about 1/3 of the performance of the slowest card in this test. If you're unfortunate enough to have purchased a NV3x based graphics card, you're out of luck with running Half Life 2 using the DX9 codepath (at any reasonable frame rates)."
The Half Life 2 GPU Roundup Part 1 reveals the oh-so unsurprising reality that to get the best from HL2, you need to buy ATI. So the other 50% of you (statistics made up) need to start saving.
" For Half Life 2, it does not seem that the extra price of the GeForce 6800 is worth it - the 6600GT does a fine job on its own and performs just as well for much less."