I kind of disagree with the idea that taller= slower and stronger and shorter= faster and weaker.
While perhaps it's a reasonable starting point, I think the two characteristics (speed and power of hit) should be linked, and you can adjust them whatever height or build you choose. The link would mean that as you raise one one you create your character or whatever, the other would be lowered.
I mean, not all tall people are lumbering monsters with fists like sledgehammers, and the shorter folk aren't all lithe, agile ninja leprechauns, no matter how cool that would be.