Well I can share my experience...I can do the same 3.7 or 3.8Ghz with 4 cores on my 720 in either Vista 64 or XP Sp3 without any changes and stability is the same.
Then I try Windows 7 and it will blue screen. 3.6 is the max I am getting stable under Windows 7. I didnt bother trying to give it more voltage as I saw no point to it.
Regards