A reputable dealer will let you take it to your mechanic for a test. Walk away if they will not.

 

I believe the biggest tires you can have before rubbing becomes a problem (at stock height, not including the Off-Road edition) are 285s or 33s.

I've done some mild off-roading, mostly through lots of packed snow and light mud. I have 265s (will go to 285s once these wear out, 3/8" of tread left) and an open differential, and I still have no problems.