If you aren't willing to trim a lot of plastic, the widest you can fit is a 10.50 wide tire without any suspension modifications. If you're willing to adjust the torsion bars to lift the front end a bit, you can get away with 11.50s.

The only person I know that runs fender flares (assuming he still owns an X) on a X is some goof ball from Northern NJ running 35x12.50s. I forget what his screen name is, first name is George. As far as I know he doesn't frequent any message boards. He signed up for ECXC last year and came out for one day. He blew a tire on a trail and didn't have a full size spare. That's a funny sight, a truck on 35s with a 30" spare.
Anyway, he used cut-out flares made for a Cherokee.

-Michael