Maybe I am not explaining myself well. I think 72" should cover your tire spread. Either size should work fine for you from the sound of it. Potholes are not like the ruts I sometimes have problems with. If your road is over 12 ft wide I would get the larger one. If not, you would have to make 2 passes anyway so no real advantage to 84". I think your tractor will pull either fine. If your gravel gets deep the larger could bog it down a little more and force you to drop to lower range. I think my results look a little better when I can keep up speed but it is not awful if I need to slow down.