Well in terms of hard numbers, I can't provide figures for everything, plus I'm not sure what figures your looking for exactly.
But I can tell you this. I've been using Vista SP1 for over a week now, and my experiences have shown that there is an increase in speed (such as responsiveness, resume from sleep, and a slightly lower memory usage). So compared to Vista prior SP1, there are performance improvements, however it's nothing grand like 30%-50% performance improvement. Simply some noticeable and appreciated speedier improvement.
Now I wouldn't go as far as saying Vista SP1 speed improvements are enough to beat out XP, let alone XP SP3. My experience with the RC version of XP SP3 has left me with the impression that XP is still running faster than Vista. However, it's nothing extreme enough to me that it would justify avoiding Vista altogether. I still stand by the recommendation of using XP for OLD hardware and Vista for NEWER hardware.
I also believe that if your going to use Vista you need to both understand and accept that it requires a larger amount of memory usage due to all the services its running and other minor performance hogs like the aero theme. I doubt Vista will ever use less memory than XP will. But once again, for NEWER hardware, I don't think the increased memory requirement that Vista has is anything TOO upsetting, just something you need to understand before hand.
For gaming, I've noticed that ATI's (I currently use an ATI card) vista drivers have generated about equal performance, and sometimes better performance (depends on the game), when compared to their XP version. I don't feel that your losing out if you game on Vista.
Just my 2 cents on the subject from my experiences.