I know exactly what you mean.
No fanatical rantings here about 400MHz G4s running rings around 2.2GHz P4s.
OS X still, apparently, has some inefficiencies in the code. I'll tell ya, Linux is very fast. Why is that Unix so much faster than what Apple's using? My B&W 350MHz G3 runs OS X, but noticeably more slowly than OS 9. OS 9 feels looser than an oily bar of soap now in comparison.
I believe the other thing the benchmarks revealed was that Moto's compilers were lacking as well. So it's not just the OS.