You can't make a blanket comparison like that. Windows 7 and 8 are faster on new hardware because of how it handles resources. Simply put, you may see a speed bump since it makes better use of your computer's resources. Yet that assumes that those resources are available. If those resources aren't available, you're either going to see no effect or performance degrade because of the additional overhead. Caching is a classic example of this. Vista and later are much more aggressive about caching data than XP. This will result in a considerable increase in performance if you have a lot of RAM. If you don't have much RAM, XP may perform better because the higher memory use of the newer OS would result in less memory being available for the cache than you'd have in the older OS. Of course, there are a lot of other improvements in recent versions of Windows that will be of great value on computers that offer the features and resources. Yet they too have drawbacks on archaic machines.