I tried a 40Mhz crystal in the Mega Midget Racer today (in place of the 36Mhz)
It causes a software crash, which I thought was a bit strange, so I put an 8Mhz instead, just to see what happened, well, sysinfo reported it as being 7.09Mhz, but it benchmarked 1451 dhrystones, while a stock 68000 does about 580.
Reason for the A600, internal ide controller, composite video out with the possibility to modify it to give s-video out, up to 2 meg chip ram, 35cm wide, whereas the A500 with A590 plugged in is 60cm wide!