Why you want XP, not Vista, for use with an OS X VM

Great series of tests by MacTech, excerpted by Apple Insider:

AppleInsider | Shootout: Parallels outperforms VMware Fusion in many tests

... 3D and HD Graphics Tests

XP: Smoothly played both 720p and 1080p videos in both environments.
Vista: Couldn't play 720p at all in Parallels. VMware Fusion stuttered on every machine except the Mac Pro. Given 720p results, MacTech didn't bother trying 1080p...

Yikes! Rules out Vista for me. You really want XP inside these VMs.

Parallels was significantly (20% range) faster than Fusion, but for me speed is less critical than reliability and stability. They didn't seem to test that.