I was previously running XP 32 on a 2.5-year-old dual-core system with 1/3 the RAM so I expect a pretty significant performance boost under any circumstances.
Most of what I've heard about Win 7 vs. Win Vista vs. Win XP is that performance is very dependent on the amount of RAM you have. Vista has a bad rep for being slow but I've been told that this can be largely overcome with enough RAM. Win 7 is supposed to have less overhead and I've read several reports that Max performs as well or better than on XP, especially the 64-bit version.
I've also heard that the version of Max you're using can make a difference. The 2010 version was supposedly optimized for Win 7 whereas earlier versions were not. I am running 2010.
Should have more to report by some time tomorrow, hopefully.