<font color=blue>I'd go with R4's. I've got them on my 33D and mow with no problems. Besides that, they look manly</font color=blue>
They do look manly!
As far as damage to your lawn, it depends on the soil & how wet it is. I have R4's on my TC18 (similar in size to a
B7500). My main reason was I didn't want to deal with tire chains.
I have sandy loam soil. We haven't had three days in a row w/o rain in over a month. Under these conditions, they do mark the ground. Of course, in some spots just me walking leaves foot prints. I've found that the damage occurs in areas that the grass is "thin". Such as in the shade of trees. Unfortunatley around the trees is where you want to turn the sharpest. On well established turf, no problems.
Something to keep in mind. Adding the FEL, a full load of dirt & the RFM on the back as a counterweight doubles the weight of my machine (from 1,500# to about 3,000#). I have to turn gently to avoid doing damage. I use MFWD when using the FEL.
There are different styles of turf tires. The ones offered on the TC18 were extra wimpy. That is they had very small lugs & voids. I feared loading them up with dirt & snow & making "slicks". I've seen bigger lugs on different brands of turf tires & may have chosen them over the r4's.
Your dealer should let you try the R4's and swap if not happy or bring a demo tractor to your house to try out.