I tried it on a new computer (Haswell desktop with SSD).
But Windows 8.1 is still slower than XP.
Even though I disabled all animations I can feel some lag between clicks and response. Probably it's because of this: http://www.youtube.com/watch?v=ay-gqx18UTM ("Windows 7 GUI slowness")
I'm going back to XP, but I needed to buy a dedicated graphics card because Intel HD doesn't have drivers for XP. And there's also 3GB RAM limit.