Moto
It appears that if you fully boot into OS4, do a warm reset and then hold both down both mouse buttons, you get some additional information at the 'Amiga Early Startup Control' screen.
Mine says:-
CPU: 604e V9.516 231 Mhz
L1 cache: 32K, L2 cache 0K
Memory: 64MB Frequency: 66 Mhz
The speed will be relevant to your question. It reminds me that I need to put in some more memory, as I've only got 22MB left after booting into OS4 :-)