I have done 5 tyre rotation for the last couple decades, works extremely well. Rotate every other oil change = every 5k miles. Identical rims, identical tyres, they all last longer and whatever you put on to fix a flat is exactly the same as what you took off. One time I blew up a sidewall and rim on Hackett Rock, I bought 2 new rims and tyres for the rear so that my lockright would be even. Since then, I've been doing a 4 tyre rotation on the remaining 3 older ones, the new ones are now approximately even amonst all 6 tyres.
Rotation schedule is: Spare to left front, left front to right front, right front to left rear, left rear to right rear, right rear to spare.
Given that, I have an "extra" 31x10.5 BFG M/T mounted on a 6 on 5.5 white steel spoker you might be interested in Bob. Approximately .25" (current) out of .65" (new) tread remaining. Trade for a case of Shiner?