I am running 15x8 Cragar Soft 8s with 4" backspacing and 37x12.5x15 Goodyear MTRs. I wouldn't have it any other way. There is no problem running an 8" wheel on a tire that calls for an 8.5"-11" wheel.
With some JKs and some wheels, the back of the wheel rubs on part of the caliper and with some they do not. I belive that some of the difference (at least on 07s) is the difference in the caliper.
Here is a pic of a JK Dana 30 caliper:
Here is a Dana 44 caliper:
The arch, thickness, and design of this piece
is different enough that I had rubbing that required grinding with the same exact wheels my friend with a Dana 30 did not. At least for 2007 models, the Dana 30 piece is somewhat rounded, while the Dana 44 piece is more of a boxed, flat piece.
Grinding the excess caliper material is no big deal. Here is the process:
I really only had to grind off material where the line is below. Not much, if any, grinding where the circles are.
I used my daughter's sidewalk chalk to cover the areas identified in the above picture. Then, I would put the wheel on with 2 lug nuts moderately tightened so I could turn the wheel and listen for rubbing. Then, I would remove the wheel and see where the chalk had been rubbed off. I ground a little material off those areas, re-applied the chalk, and repeat. After repeating a second time, I had elminated all the scraping/rubbing on the drivers's side. The process was the same for the passenger's side.
After I finished, I painted the areas I ground with some grey anti-rust primer paint.
Hod rod builders have been grinding calipers for years. I have not heard of one problem here or on any other forum for those who had to do a little grinding to make 15" Cragar Soft 8s with 4" backspacing fit.
Here is my rig:
My wife driving: