I've found that with my quad I don't really want a huge amount of tongue weight, as a big log can take so much weight off the front tires that it can become hard to steer, especially on hills.
I'm going to be building some kind of log arch rig over this coming year, I'm getting tired of either having to debark logs with an axe and draw knife OR risk chewing up chains with sand and grit. Got my eye on a discarded truck rear end axle that someone ditched a couple miles away down a backroad. It even has near-new tires and rims on it!