In PNW terrain I've had no issues with the sidewalls on my GY Duratracs (315/75-R16) even when aired down to 8lbs. Our terrain is primarily dirt, mud, tree roots, and smoother rocks. We do have plenty of downed tree branches that you'd think would cause more of an issue. I love them for snow wheeling. The guys that I have seen ripping sidewalls up here are the ones that also break stuff every trip from driving the trails like a pissed off teenager at the wheel someone else's truck.
As far as GY MTR-Ks being constantly out of stock... It seems guys up here order a couple sets at a time to stockpile them. These would be the same group as the above. Guys initially stockpiled them because they were hard to get, now they are hard to get because these same people keep stockpiling them.
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These threads always amaze me when the inevitable lift and tire spacer discussions enter the conversation. For every guy who swears by the spacers there is another warning against them. Same goes for budget boosts. I bought one as a temporary measure while deciding what lift I really wanted to go with and haven't found a compelling reason to upgrade since it gets the job done and does just fine on the trail. A super flexy suspension is kind of a waste for mainly overland style wheeling with only a few weekends a year doing off road parks. If you can afford it and want to do it then more power to you but don't let someone tell you it is necessary.