"Sure we can derail the thread further and make other arguments but you won't be negating the original point at all, newer operating systems from Microsoft are almost always slower than the previous version, it's simple bloat."
This of course is nonsense. If you want to make an apples to apple comparison of XP and vista after installing XP install desktop search and windows defender (both are standard in vista), install your favorite antivirus software on both, and you'd have to turn off Aero on vista. You'll note that in both of your test hardware comparisons vista SP1 will benchmark faster or equal to the XP system. If you want to compare it the other way turn off desktop search in vista, turn off aero and disable defender. Again you'll find that in both cases vista sp1 will benchmark faster or equal. And if you really want to see the difference add any office apps you like and start timing how each system performs under load. There are some quite specific areas that XP still beats vista (copying files on the same disk XP, appears to do this alot faster for some reason), however transfer that same batch of files over the network and XP gets crushed (particulary when transfering to a linux or vista system).
You can call the extra features vista brings bloat, but, oddly enough, the users still want them (and those that don't can turn them off).