65816 is much more cycle efficient than 68K... as long as your using 16 bit data and relatively simple instruction, it can be even more than 2 times the speed of an 68000... however, 68000 is much faster on 32 bit ops and has more registers and more instructions... it's a better chip, no doubt, but a well optimized code for the 65816 will FLY!!!
I would also think that the 65816 programmers would have to struggle with the same type of segmented memory architecture issues that DOS and early windows and OS/2 programmers had to deal with when trying work with more than 64K RAM.
