As you compare native vs. emulator. perhaps it would be nice other comparatives as native windows (XP & Vista) vs. Xen, Virtual Box, and Wmware installations.
And for a good an fair comparation as VB and Wm has windows and linux versions, compare
winXP native vs winXP virtual in XP vs winXP virtual in Vista vs Linux virtual.
And for further benchs a test only with opengl games and games with 2 versions as Id software titles.
I've read that Xp runs faster virtuali than native (becouse of no need for antivirus programs).