Ok as one of the only people I know of who has worn a set out I will reply
I have 31x10.5x15 and I am just over 30,000 on them and 10k of that was with a welded rear and lots of rotations I rotated about ever 3k.
DIG IT!
I've got about 10K on mime. Started w/ 19/32, have 13/32 of tread left. I do a 5 tire rotation at every oil change. Running 29 psi. I figure I will get 30 to 40K out of them. HTH Jim.