I can only tell you about my experiences with a Core2Quad Q6600 on VMWare Fusion 3.0. I have three boot partitions on this system (ahem yes it is a hackintosh running with the E-Fix USB).
So i can do performance measurements. I use it for sometimes very large compiler sessions. And the amazing fact was that Linux as a Guest runs without any measureable time difference on virtualised and native Linux. Windows7 on the other hand only runs with 40% on my machine and GUI is allmost non useable while the GNOME Desktop from latest Ubuntu still works fine.
Check this out. Virtual Box is free so there is nothing to loose.