I'm currently running 5 wow's on a AMD BE-2300 (2x 2.1G procs) and a HD2600xt

using the Lo-res macro, setting Maxfps to 15, and disabling the audio on slaves gives me about 25-30 FPS on my "main" - but about 10fps in cities

Upgrading to 4GB ram did very little for my FPS so i'm guessing my proc is the bottleneck at this point.