> It is thought that processor boards clocked <500MHz may (as a rule of thumb) use
> MPC7400/7410 processors, whereas those clocked higher may use MPC7450.

Please read more carefully what pega-1 actually wrote regarding that matter. In fact, he corrected his former misleading statement which said that expected MorphOS support could be linked to clock frequency being <500 MHz or >=500 MHz. As I outlined, both PowerMac3,1 and PowerMac3,3 have models with 500 MHz MPC7400, and PowerMac3,4 has model with 533 MHz MPC7410. That's what pega-1 had overlooked before. So if you really want do draw a frequency line it would have to be somewhere between 533 MHz (maximum for MPC7400/MPC7410) and 667 MHz (minimum for MPC7450/MPC7455), for instance at 600 MHz.