I would not even think of moving to Vista until the hardware that will "run Vista screamingly fast" drops down to that price range.
I've always installed MS operating systems about 2-3 years after they come on the market. But I will pass on Vista regardless because of (1) the DRM issue and (2) the lack of any compelling features in Vista.
Vista should run screamingly fast with your setup, well depending on the gpu. But installing a OS after a year or two of its first release is always a good idea, I however just love being an early adopter.