I have 33x12.5's on the stock 7" rim...with no problems.

Lots of people run 33x12.5's on 8" rims, also w/no problems.

For a street application, the wider rim is more stable, but for the X and off road, a good sidewall bulge is fine, and even with the 7" rims, the bulge is merely subtle, not large.

For 33x10.5's, the 8" rim is fine and dandy eitherway...I'd get the 8" rims, it gives you room for expansion, and will hold the 10.5's with plenty to spare.

Wider rims also impact your turning radius, etc...so the X doesn't like too wide a rim anyway.

Also - you want 5.25" of backspacing and 40 mm of offset, or as close to that as you can get.