The Motorola and/or IBM processors that go into Macs have historically sometimes been faster than the Intel and/or Intel clones that were going into PCs of the same vintage, and at other times have been trailing behind.
When the G3 was new, it kicked Intel ass thoroughly enough to prompt an ad campaign that featured scorched Intel bunnies, a parody of an Intel Inside ad that featured bunnies.
Now we who are of the Mac persuasion are seeing our platform getting its ass kicked by faster PC processors. I think this is largely because AMD scared the bejeezus out of Intel and they dumped their assets into speed development trying to stay at least within reaching distance of the Athlon, and AMD had to stay ahead of Intel to compete effectively so it did likewise.
People who know more about chips and instruction sets than I do say that this is nothing short of a miracle, but economics of scale produce miracles. They still say the PowerPC architecture should scale better in the long run, and that pushing around the vintage x86 instruction set as native hardware code is a massive handicap.
(They say: The modern Pentium and Athlon chips are CISC only in emulation. They are phenomenally efficient pseudo-RISC chips much like PowerPC chips are, but the stuff they deal with is RISC-like decoded x86 instructions that were decoded earlier in the pipeline. The OS and application code is still compiled for the x86 instruction set and the chip itself has to translate it on-the-fly and rip it apart into smaller equally-sized segments of RISC-type persuasion before it can tend to them. One wonders what Intel could do with a raw RISC instruction set. Applause for Intel. Those folks do some incredible stuff with chips).
Meanwhile, most CPU’s sit around twiddling their virtual thumbs waiting for some instructions to come their way, because there are other bottlenecks keeping CPUs from being fed as fast as they can eat. For the overwhelming majority of things you do on a computer, a hypothetical 8 GHz processor would not make anywhere near as much difference as you might think. Definitely not as much as doubling the system bus, or doubling the seek and read and write speeds of your drive. Not too long ago, I upgraded my processor from a 300 G3 to a 500 G3. Much more recently, I swapped out my Toshiba 18G for an IBM TravelStar 60, which is a very fast laptop hard drive. I got much more of a noticeable performance increase from the hard drive upgrade.
The faster RAM architectures that manufacturers (mainly PC, I’m afraid) have been playing with should also result in increased ability to feed the CPU chip. (In all fairness to the Mac, I think the fast L1, L2, and L3 caches have generally been superior to their PC equivalents which is part of the reason we get more bang for each MHz of CPU, and faster RAM will not eliminate that disparity by itself).
People with a greater understanding or more current data are welcome to correct me here on anything I’ve said.