The one detail you forgot to mention is what width you are going with. > 3.75BS sets up the tire differently depending if its a 7" or 8" rim, 8" will stick out further. You cannot use the backspacing number as a comparison with different widths.
I've been running with outlaw II rims since the beginning, 15x7 3.75 BS (-6mm Offset), and now I am also running with BFG AT 31x10.5x15. With the stock tires, I had to trim the mudflap area as well as the front plastic, with the 31's, I had to nibble a bit more and since I had installed AAL's, I had already cranked the T-bars. My tires barely sticks out from the fender, looking straight down, you cannot see the thread of the tire.
FYI, I have a whole set of trim pics on my site for both sets of tires with my rims.