|"will win 7 give better performance than xp."|
I think that Win 7 would give you better performance than XP on your machine. It's definitely smarter than XP when it comes to juggling processor cores.
I used to dual boot XP and Vista on a 3.2GHz Opteron X2 machine, but I now run a single OS--Windows 7 x64--on that computer.
-I found that, while my handful of ancient DirectX 7-8 games were a little slower under Windows 7, my DX9-10 games were just as fast as they were under XP and Vista.
-On Win7, 3DMark06 scored around 100 points higher than it did on XP, and nearly 400 points higher than Vista.
-If you're into photo/video/design and use Adobe, you'll notice right off the bat that CS4/CS5 applications run a lot more smoothly under Win7 than they do on XP.
Super PIII | Unlocked ES Tualatin @ 1.8GHz (150x12, 1.65v, 512K L2)
2GB PC2700 | 500GB | Radeon x1950Pro | Apollo Pro 266T | Win 7 Pro