The difference between the emulator in the early vs. later (PCI) PowerMacs is the later version uses dynamic recompilation combined with caching while the early version was strictly iterative.

Another note regarding the parallel thread going on right now about "Road Apples": one of the reasons the original 5200/6200 Performas generated so much hate is the original 603 (not 603e/ev) CPU didn't have enough onboard cache to keep the emulator happy (it had only 1/2 the total cache of the 601). They also had only half the bus width of the original 601 machines (6100/7100/8100), so those two factors made them uniquely sucky, arguably even worse than a Quadra with a 601 upgrade. (Clock for clock, anyway.)