The P4 is pretty lame... The G5 will be at least as fast if not quite a bit faster... If you had an Athlon64 or a CoreDuo then they would piss all over the G5
CoreDuo yes its faster but...
Athlon64??? maybe you mean the AthlonX2 ??
because my brother has an Athlon64FX@3200Mhz and I have a DUAL1.5Ghz G4 and I am 2 times faster in almost everything....
ofcourse athlon is running WinXP64 and I'm running OSX, but I don't think that an OS can make such a difference anyway...
EDIT: I think in INTEGER mulithreaded operations we must be at about the same speed, but in video encodings like H.264 and renderings I'm about 2x faster..
maybe thats because of 4 altivec units that my machine has..(2 altivecs per cpu)