I don't know where you are, F-350, but I know Nebraska sure is a lot different than back in PA. I've run into the ethanol plant near 100K on 5 axles regularly. The highway's flat, you just let off the throttle and let the engine brake work a little longer. Never could get away with that back east. Only trouble is, the large cars that come into town behind you, just as heavy, and don't think far enough ahead to not burn their own brakes up.
Unless width precluded it, I'd probably just get the 7K car hauler, too. I had over 5K (after chains and binders) on a bumper pull behind a V6 half ton Chevy. It knew the weight was back there, but with that little motor stopping was less a concern than getting going. I kept it on the back roads with that load.
We have three gooseneck stock trailers at work. With the prodigy controller in the one duramax, you can say that none of them have working brakes. You just have to look forward past the end of your hood, and past the rear bumper of any car ahead of you. If you can't see past him, you back off to where you have plenty room to easily stop if he does.
Can't wait to read the heck I catch over this one.