You can't overclock the fpu. It will simply won't function properly when it's overclocked.
Since the 030 got so little cache (the part that benefits from overclocking) the DRAM will choke it so much you won't notice any difference.
On the other hand, buying a 060 50MHz accelerator will speed up your system significantly because it got a huge cache (for a 68K anyway) and internal fpu. The difference in speed between 030 and 060 using identical clocking is substantial.
