The new Athlons64 has a frontside buss of 1000mhz, the new Powermacs have a frontside buss of 1250mhz
In the case of the Athlons they dont even need a memory controler as it's built into the processor.
here are some quotes
Bandwidth to Burn
The Power Mac G5’s ultra-high bandwidth system architecture features up to a 1.25GHz frontside bus — one on each processor — for maximum throughput from the system to the G5 processor. And a point-to-point system controller lets data move directly between subsystems, without affecting processor function.
AMD has introduced its new dual channel Socket 939 Athlon64 platform just a few weeks before Intel's new architecture launch. Our benchmarks show what AMD's socket 939 brings to the table, with such features as a HyperTransport speed of 1 GHz, and how its performance matches up to its price.