I spent maybe half an hour trying to pull an oak a bit under 3" with my 25 hp 2500 base weight tractor, using cable grips on an adapter on the FEL. I'm wrapping a few turns of 5/16" cable around the trunk at least two feet above ground level, having already cut the tree above this level. I was shifting it plenty but didn't get it out. I was getting one or the other rear to come off the ground slightly, which could get scary except I'm operating in the lowest gear and I don't think I'm lifting them an inch before I can clutch and let them down. My rears are filled and I could add an 800 lb ballast box, but this also sounds like it could get hard on the equipment. Oaks are more difficult that way, I think, and our ground is this awful bank gravel cemented together with clay. I pulled the cable out of the clamps several times and am breaking strands, though I have a good amount of cable available. But I had to stop, not enough time. Will get another chance Monday morning, and I might start pouring some water into the gap around the tree to lubricate the whole operation.
Maybe I can shower myself with mud in the process. If anything amusing results, I promise to post.