I made some tests on Mac mini 1.5GHz and PB 1.67GHz (5,9 - A1139), and noticed quite some difference between OS versions on the very same machine, which may explain some results.

Mini with 3.19: 13.56s
Mini with 3.20: 5.23s
PB with 3.19: 13.72s
PB with 3.20: 5.88s

Funny that Mini is slightly faster than PB, but quite similar anyway. I'll try to test with some G5 machine(s) later in the evening or so.

BTW. can you make the test without using any Rnd functions, using other kind of calculations? Or share the source code for experiments?