O.k. did you move the numbers the other way now?

G5 (AGP) 2.3GHz: 3.438s
PB5.9 1.67GHz: 6.329

What kind of G5 are you running?
Are you sure it runs at full clock? Maybe test something else like unpacking a big archive.

This has been a bug with at least the iMac a few years back (which I noticed when unpacking the beta ISO vs an 1.8GHz G4).