at 200MHz, the 604 is ~27 MIPS faster BUT the a4000 because of it's design allowed for a more faster ppc subsystem, so all benchmarks regarding memory read/write etc, are 2X the speed on the 4000... a 604 on the 1200 would not help...
CS PPC has 64bit memory, BPPC 32bit. That's why CS PPC has 2x memory speed.
AFAIK the reason for 603 only for BPPC is temperature considerations, and PCB real-estate. Even as-is with 603, the BPPC is unbeliveably crammed.
