I run a 2.25 Crossmark at the rear on my 5c and there is plenty of clearance for that. TBH if you are wanting to run any bigger than that I would point you towards a 575.
As for the 5c it is a fantastic bike. All the reviews, particularly the comments about it leaving you as a hollowed out shell are spot on. The suspension has a very invisible feel to it, it gets on with its job without you feeling what it is doing. Also, the stiffness to weight ratio of the frame in general is absolutely astonishing. It’s a bike you feel very much “in” as well, possibly because of the lowish BB height. This makes it a very involving ride.
I was intending to use this for racing and faster smoother trails and keep the 575 for the rockier stuff, but since I got the 5c back in Jan I haven’t ridden the 575.