Just before I start talking about windows 7 and performance, I will give you guys the spec's of my machine that I 5 box on.

ASUS P5B deluxe WIFI-AP mb
Intel Q6600 Core 2 Duo running at stock speed
8Gb ram
2x nVidia Geforce 8800GTS (684Mb video ram) in SLi mode
3 monitors (2x19" and 1x22")
2x320Gb SATA I hdd's
2x1Tb SATA II hdd's

My multi-box wow's are all setup on one of the sata 2 drives and the copy of wow that I use for solo boxing is on one of the 320's.

I tried 5 boxing on XP with 6Gb of ram installed but because it is a 32bit OS, it only saw the first 4Gb's and the video cards are taking approx 1.5Gb of ram out of that.

It was damned slow and gluggy with that setup.

I tried Windows 7 RC1 32bit with the same sorts of results. Very slow and unresponsive when 5 boxing. 3 boxing wasnt a problem.

When I stepped up to Windows 7 RC1 64bit and added in another 2Gb of ram is when I started noticing things start jumping. I still lose the 1.5Gb but my effective usable ram is not 6.5Gb and I have noticed that the games are running a bit smoother. The only problem that I have is that with my monitor setup, the two 19" monitors are analog (DB15) and the 22" is DVI which are running in different resolutions (1400x900 and 1650x1080) which does tend to screw up the frame rates. I will be looking at going to 3x22" monitors at some point in the future with a multi-monitor stand that lets me rotate the 2 side monitors into portrait mode.

But in terms of performance, I have found that windows 7 is a lot smoother than vista or xp and will happily run wow on my desktop easily as well as on my laptop.