RC5 depends heavily on specific bitwise rotation instructions, which are rarely used by anything else. The figures on that page don't tell you anything other than how fast those chips can run the RC5 client.
As I recall the old AMD K5 was a superstar at RC5 despite being an otherwise lacklustre processor simply because the instructions that RC5 executes repeatedly worked very quickly on the K5 core.
On the vast majority of tasks a modern x86 processor will crush a G4, if only because PPC systems tend to have poor infrastructure surrounding the CPU (PC133 memory, slow busses, etc).
I think we need to accept that and move on. CPU speed is no longer a critical factor in how useful a machine is anyway.
