MacRumors has reports of PowerMac G5 benchmarks. I actually downloaded a few different benchmark tools last week and ran them on my PowerBook so I could compare the results to the Quad when it arrives.
g5 G4 1.5ghz with 1.5GB of RAM and a 5400 rpm HD scores a 38.49, directly after a fresh boot. The Quad is supposedly scoring in the 160 range – I think I’m gonna like this new machine. 🙂