ArmA II Comprehensive i7 Benchmark XP vs. Win 7

Very interesting reading.

Microsoft went the whole cosmetic hog with Vista and the average hit on applications and games turned in at around a 15% performance Hit.

They improve on this slightly by roughly halving that with the introduction of Windows 7 but it's still no match for the 'soon to be out of support' XP.
Personally, I intend to stick with XP 64 as long as humanly possible as it's everything you could need in an OS and allows you to have more than 3gb of RAM.

What we need is profile presets for Windows 7 - similar to those in the Nvidia drivers which will deliver the maximum performance by disabling things we really don't care about.