Nice looking job, a log arch is one of the best tools I have for firewood and fence posts. I use mine behind the ATV, it was built to follow in the ATV tracks.
You might find a set of deflectors in front of the wheels very handy. I added mine after a year or so of getting hung up on trees in tight corners. Now the arch just bounces to one side when you hit a tree, and keeps on going.
Where you mount the axles plays a big factor in weight distribution when you have a log hung from the arch. Mine are about 8 inches behind the arch, and actually add weight to the hitch when loaded.
I've been contemplating a bigger version for use behind the tractor, but for the stuff I cut the ATV is a lot more nimble around the woods. I've had wood up to about 16 inches on mine and it handles it with no problems. I used Chrysler stub axles, and 1.5 inch x 1/8 square tube for most of it. The boat winch is used for bigger stuff, small wood I can handle.
You can actually back up to the log, disconnect the arch and pivot it so the tongue is upright, then hook the choker and use the tongue for leverage to pull the log off the ground. Works very well.
Sean