For us fellow Mac enthusiasts and your own curiosity, you should do the following.
Download
Xbench 1.1 and benchmark it. You can upload your results to the Xbench site, I do believe...And the more on there, a better idea of the average performance we can get.
Also,
PS7 Bench
And you'd be awesome if you could get us UT, Quake 3, or UTk3 fps info.
I'm considering buying UTk3, opening the package in CompUSA, installing it there, and doing the benchmark...But that would be harder than you doing it, right?
Now if you're really good, Xbench 1.1 is open source, so if my understanding is right, you could possibly recompile it with IBM's new beta compilers optimized for the G5. But I'm really not knowledgeable about this stuff...I really should learn a "real" programming language sometime...
Anyway, congrats & best wishes on the new G5. Enjoy it! Benchmark it! Love it!