One of our Wales UK-based members has reported receiving his Power Mac G5 Quad earlier in the week, and has run a preliminary set of Xbench 1.2 benchmarks on it.
While full details are in the forum thread, the overall Xbench score for the machine with 3 GB RAM running Mac OS X 10.4.2 weighs in at 151.86.
For comparison, the Dual 2.7GHz PowerMac has an Xbench score of 109.87... but due to version differences and other confounding variables, it is hard to draw many conclusions from these Xbench scores.
Cinebench 2003 scores were also posted: Quad 2.5GHz Power Mac compared to the old Dual 2.7GHz Power Mac