That's all good and pretty, but it lacks the GPU rendering stuff that Vista has, and IMO it makes a BIG difference to performance.
For example, I have my desktop and laptop, both with Vista installed. Glass can't run on the laptop because the IGP is....crap. WEI has them both clocked around the same, with the laptop having a better processor and memory score, whilst the desktop has a much better graphics score and a better HDD score.
Even with aero glass running on my desktop, it runs faster than the laptop, despite the fact that the core areas (Processor and RAM (Laptop has 1.2GB, Desktop has 1GB)) are better, and glass et al isn't running to chew up cycles for rendering pretty UI elements.
All I can put it down to is Vista offloading lots to the GPU does make a considerable difference. So while XP may look pretty with Flip 3D and all the rest of it, the performance gains will come with Vista and how it handles the processing of those tasks.
On a side note, I still love XP. Vista is great, but there are just some things that XP does and it does them very well, so much so that I can't talk bad about it.