I haven't had any heavy flex. most of my offroad is sand and dirtroads, no rocks. that being said they rub a little backing up at full lock so there is no doubt they would hit if i did push it. i do have bmc as well.
Duratracs 315 70 17, roughly a little under 35x12.5
I have been pretty happy with them but am tempted to go down to 33's. I do a lot of road trips in the car and am thinking the road manners would be a little better with minimal loss in clearance.