Anybody here ever worked with a 6502?

I've got a project coming up that required conversion of an existing product (written in assembly on a 2Mhz 6502) to a new core (8051) with a few various additions.

This product contains a LOT of math, although the math has scaled precision and uses a few lookup tables. I've glanced over the instruction set for the 6502 and it doesn't look that bad.

Say for instance, I have an 8051 (original 12 cycl per instruction).

Two things I need to gain a grasp on such that my controller selection is sufficient is "speed", and "size due to instruction set".

How does execution speed compare? I know the original 8051 is somewhere around .1 MIPS right?

Second, for example if I wrote a routine to multiply a 64 bit number by another 64 bit number on both controllers. Would there be a LARGE difference between the two (size and speed wise)?

Thanks to any information that can help me get a feel for the 6502.

J