Maybe a misleading title, but I wasn't sure how to word it. Anyway I read on another forum and dx10 ultra high users can run crysis in dx9 mode with the same (well almost) very high graphics as in vista and get a performance boost.
I don't have vista so I could not test, here is the thread:
http://www.overclock.net/pc-games/25...x-10-dx-4.html EDIT: original thread http://incrysis.com/forums/viewtopic...236267#p236267
Here a guy made a rar files with the tweaked crvar files, please read that thread for full details/ instructions. I am not responsible for anything that may happen

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http://www.overclock.net/pc-games/25...ml#post2909412
Supposedly some people nearly double their frame rates (10fps -> 20fps, another person 15fps->30fps) and claim the game looks the same (going from dx10 vista to modded cvars on dx9 xp)