As far as I know, 68030's were sold at 16, 20(?), 25, 33, 40 and 50MHz.
There wasn't a lot of overclocking room, some folks have got 50MHz parts to run at 60MHz I think. Trying to run a 25MHz 030 at 50MHz is not going to end well.
33MHz pieces usually run very well at 50MHz (at least the PLCC package). That's a 50% increase. The 68882 is very overclockable, usually twice the rated clock speed is no problem at all.
