Backspacing Question...

I bought my XJ with stock steel 5 spoke wheels and 30x9.5 tires. I noticed that the rears are slightly rubbing on the inside. Does anyone know the backspacing on these stock wheels?

Also

I want to buy a set of Allied Daytona Wheels but I am unsure which backspacing I need. (3.75, 4.00, 4.75) I want to push the rims out as far as possible to avoid any rubbing on the inside. But, at the same time not too far out because im going to be buying 31x10.5 M/T's soon and I dont want them to rub my fenders when it flexes.

I've got a set of Ravine wheels which are a factory 15x8 and 5.5 inches of backspacing. I have 33x12.50s and they do not rub at all. The rears are within an inch of hitting the leaf springs but the fronts do not touch the control arms at all. (At full turn)

Running only a 10.5 wide tire> my opinion is that I would run a 4.5 to 4.75 backspacing. Just my thoughts......