The 315/75/16 at/ko is a good tire. I've put almost 60k on a set, mostly on road, snow and ice is decent new, but you'll want to run a hot knife over them later, and the sidewalls are decent as long as you're not spending all your time dragging them over sharp rocks.
Speaking of which, I have four with a little tread above the wear bars, they'd probably do fine for spares, but all have very slow leaks...like a couple psi a week...and one unused spare. When I get new tires (which will be soon), the four used at/kos are up for grabs if anybody wants a free as-is 35" spare. I don't know what I'm doing with the unused spare, it's almost 7 years old at this point, but full tread etc...
'00 Project, constant state of (d)evolution