Why does Dolphin run faster on WinXP than on Win64

[themanuel]

So the last I did was to update absolutely everything: nVidia driver, DirectX (was updated already), VB runtime and Windows. Only VB was significantly out of date. I did not see any improvement with the recent versions of Dolphin although the old x64 version I'm using with Win7 seems a bit more consistent now with its framerate so I'm back to to where I was with Win XP.

I still can't explain why the x86 version runs better in Windows XP than on Win7 by a good margin and feel that if I find something there, it could yield further optimization of the x64 version.