Well, I moved three more logs today. The largest was 17' by 22". Again, not even a hiccup from the tractor. I got to try the rear differential lock when one rear wheel started slipping. The lock did the trick and the tractor kept on moving. I even figured out that I was "over engineering" the chain lashing and greatly simplified the way I do it.
The log rig on my 3PH is locally made. I bought it from KiotiDave of Upper Valley Tractor in Enfield, NH.