So how much room is there behind the tire.?

235/60's are just a touch wider than the 225/55, but you don't lose any height..

If you think the 28" tall tire looks small in there now, wait until you go 27"
(unless that is part of the look you want..)
215/65 = 28 x 8.7 (what came stock)
225/55 = 26.8 x 9.2
235/60 = 28.1 x 9.45

I want to go with
255/65 = 30.08 x 10.2
265/65 = 30.5 x 10.7
what I really want are:
265/70 = 31.6 x 10.7
but I don't know if these will fit..
(I will probably have to put spacers on to get any of them to fit..)