Why does Dolphin run faster on WinXP than on Win64

[themanuel]

I'm dual booting my PC on both OS's. The exact same x86 version of Dolphin runs 15-20% slower on Windows 7 than it does on Windows XP.

At first I noticed that on Windows 7 I would not get any screen tear with v-sync turned off so I figured maybe the Aero theme was forcing v-sync even though I had it turned off in the emu. I switched to the Basic theme and sure enough, there was lots of screen tear but the game speed did not improve at all.

I normally run the x64 version of Dolphin on Win7 which is a bit slower than the x86 version on Windows XP but if I find why Windows XP can run the x86 version faster, then maybe I can improve the speed of the x64 version as well.