I don't know why, but I have much better FPS in Crysis using DX10.

Settings:
Textures, Water, and Sound are all Very High
Shaders, Objects, and Particles are all Medium.
Everything else is High.

I get 35FPS pretty consistently.

On XP I have the same settings only without the Very Highs, and I get around 30FPS.

I found this pretty odd, and I'm guessing it's a driver issue. I have Vista on the latest 185.xx and XP on manufacturer's preset since the latest drivers wouldn't work.

 

It only makes sense, XP is about as stretched as it's ever going to get for performance. Vista still is young so there should be a decent amount of improvements available for drivers.
Also, DX10 is more efficient than DX9 (when coded properly).

 

If the XP drivers are older than 180, that could be the cause. 180s show a decent improvement in performance than older drivers.

 

For some reason when I installed the latest drivers from LV2G on XP they didn't work at all. It put me in low-res, 4-bit mode. I made sure they were 32-bit and for XP. I also tried the drivers before that, but everything was terribly laggy in general use. I didn't even dare try them in-game.

 

In Far Cry 2 i also get more FPS in DX10 compare to DX9

 

I don't know how you're measuring this, of course, but 30fps strikes me as extremely low. Using the in-game benchmark with those settings, I get an average fps of 36 in non-SLI mode, and running around in the Island level I'm usually in the forties.

I'm guessing it's an XP driver issue.

 

I use the "r_DisplayInfo = 1" console command to show the info. Where's the in-game benchmark?

 

Program Files/Electronic Arts/Crytek/Crysis/Bin 32/Benchmark_GPU.bat

The benchmark runs with whatever settings you last saved in the game.