Since you made a claim on PPC vs X86 I'm restarting PowerPC vs X86.
You're comparing 2003 machines to 2006 machine and are what - surprised?
There are plenty of benchmarks on this, but x86 are stronger in some areas (branchy integer stuff) while PPCs are better in different areas FP and especially Altivec.
Apple were very clever with the timing of their switch because it meant they went from lat year's PPCs to next years x86s and of course the x86s were faster.
Actually according to the benchmarks published at the time there wasn't that much of a difference between them, in fact the G4s could rip music faster than the first mac x86s.
It was only after the Core2Duos appeared that a clear gap emerged, but by then development of desktop PPCs had already stalled.