GTX 460/DX9 on XP

Hi guys.

Windows 7 was really pissing me off with the lack of compatibility for older games so i formatted and went back to good old XP. Now i'm worried that when i come to play newer games i might have problems. If i use DX9 on a DX11 card will it perform slower or will it just not look as nice? Also i have heard that DX10 is possible on XP with some sort of unofficial patch but there are a lot of fake ones out there, anyone got a link to a decent one?

Thanks in advance :)