What is your configuration of the PC and the software you wish to install??
If u concentrate on speed I recommend you to remain on XP...
On testfreaks.com, Editor Kristofer Brozio says...
"To me, it looks as though Windows Xp is still the best choice for an operating system. Sure the others look nicer, but in terms of performance I think Xp is the one to go with on average. Yes Vista and 7 have DirectX 10, but how much of a difference does that really make? Vista and 7 have Aero, but again that just makes things look nice, they’re nice tweaks and little improvements to usability but in terms of performance it doesn’t do much except maybe hinder it.
Maybe I could turn Aero off and see what kind of results I get then? I’ve always wondered what kind of impact it has on the system."
Windows Xp vs Vista vs 7 - Benchmark Test