I also have a quadruple boot configuration, Vista X86 which is still my main OS, Vista X64 mainly for one game I do development for, Windows 7 RC X64 and Leopard 10.5.7.
There is only a small difference in performance tbh, in fact the reason why I have that second Vista partition is because the game I do development for (GTAIV) runs a lot faster on Vista then on Windows 7. It used to be the same, but since Win7 RC, there is no way I can get the same fps then under Vista, hence the reason I use that for the game.
The 7 build I am currently using is 16384, didn't install the latest.
Vista was/is a great OS, and yeah I will be replacing most of my machines with Windows 7, as I think the aero improvements make it worth my while.