Great info Bill!
I think the largest limiting factor on these Ford/Mercs are the bumper-integrated towing hitches. They're flimsy. Once you get a CL III bolted up to the frame, you've substantially mitigated the towing limitations of the factory CL I/II systems.
They're plenty capable towing rigs once you get around those 'cute' bumper hitches. Gear ratio should certainly be considered if you live in a hilly/mountainous area. I'm out here in the midwest, and as far as I can tell the world is still flat from my view.
Also should add that we're seeing about 16MPG with our setup and traveling 60-65 max on the highway.