Just to be pedantic, if it's a clone of the 8 bit PICs, then one instruction takes 4 clock cycles, so a 20MHz clock should be considered 5MHz if you're trying to compare operations per second.
that's a good point! i wondered about that, but i don't have the chip yet, so i checked the datasheet. the datasheet lists a cycle count for each instruction, and as i said, most instructions are 1 cycle
on the other hand, something like a 32-bit multiplication or a floating-point subtraction is going to cost a lot of instructions, if you can afford it at all
