I’ve no experience of the rhythm forks, but know rockshox MC damping pretty well and have a set of 32SC performance forks with the grip damper.
I’d say the grip damper is about as responsive to the MC damper, but where it is miles better is control and anti dive. earlier MC’s would dive horribly and although RS did improve this a bit, there’s a reason MC is found on more budget models.
from a stiffness perspective, the recon shares the same chassis as many of the older models, they’re stiff enough not to find them wandery, probably on par with the SC fox I have, maybe the fox is a little stiffer than my previous SID’s and REBA’s.
anecdotally, I have read on several places that the fit4 damper is a little more ‘XC’ than the grip damper, in that it’s a bit less supple over small ripples, but I’ve not ridden one.