rim and tire size

i was reading in the search archives about rims, tires, and backspacing. it was said that 8" rims should be for tires 33 and bigger, and 7 "(stock) for tires under 33. i was getting ready to by some 15x8 rockcrawlers for my 31x11.5 LTB's. i plan on going to 35's later when the lift ever gets done. but the question is, should i stick with stock rims for now and get the rims when i get the tires?

I run 32x11.5x15 on a 15x8 rim. Works perfectly. But if you want to save money use the stock.

I ran 31 10.50s on 15x8 rim and had no problems