Gromit, I don't have a hack on my RE but I do have a Solo seat.. As far as movement goes the solo should be just as good if not better, I have mine set up where it sits lower than stock and seat itself is narrower in the front. This I believe allows a slightly better range of motion.
I would recommend a solo any day, as I find the sprung seat much better on rides over 30 minutes. After about 2 weeks that stock sucker felt like a brick. You could always try one and switch back.