I'm sorry to tell you folks, but I just came back from comparing both games for jumping ability, and Mercer outclasses Heller by at least 2 floors. Heller can clear 6 floors with full upgrades, and Mercer clears 8, coming up level with the 9th floor. Heller's wall jump looks better, not higher but a better simulation, but I have yet to find a way to gauge it. Probably about the same, I'd guess. The camera is focused closer to Heller than Mercer, making Heller's world a little larger than Mercer's, but it's strictly a POV thing.
I haven't checked apparent running speed yet, but clearly Mercer's air dash is also superior, which is most likely the reason for Heller's extra dash. Heller seems able to go farther, but again I believe it's just point of view coupled with subtle animation touches: the sound of him gliding, the wispy trail of energy that changes angles as he rises and falls, that sort of thing.
So for those of you who laughed at those who didn't like Heller's jump, be ashamed that you didn't check these features out before mouthing off.