In GA your fine with the current driver license and probably for other states as well.  I use a MDT for pulling and have been ok with regular license since tagged in ga, even through other states (including TX/OK).

The 450,550's are crap on mileage.  They normally have 4.30 gears or lower so fuel mileage suffers.  Friend of mine gets 6-7 mpg with a 2007 450.  Not much better unloaded.  My 4400 international gets 7-8 pulling and 10 unloaded.  Not much difference here but I stop better than he does.  Also my truck is not over loaded at all.

I pulled similar trailer for years in ga and about the same size as yours.  I would not buy something bigger for that size of trailer.  With a bigger truck yes you get bigger brakes and gearing but other than that they are pretty much the same truck.  The 450-550's ride is alot more stiff than the 350. 

Just my opinion but I would not go up to a 550.  Resale is not very good on the 450, 550, 4500's at all.  I looked over this issue for more than a year before getting the 4400IH.

570.  The mileage would be alot better if I would keep it under 2k rpm.  I have trouble with that though.  closer I get home faster I run.  i am working on it, and exxon mobile has decided to start helping me.  i started out good yesterday going down i-10 at 70mph.  100miles from home it went up considerably.  i would like to and probably may start driving 65 again just to save some fuel.  problem being is that when you run slow in the hills it kills upward momentum in the climb.  hence the reason running down hill i let it eat and run up the other side instead of climbing at 45. 

the trailer is tad heavy too, not so big but heavy.  32'floor but weighs 17k without the horses.

Let's see 100 gallons of fuel on board, 75 mph yields 6 mpg, 65 mph yields 7 mpg, so 1 mile per gallon difference into 100 gallons = 100 miles at 7 mpg at a cost of 4.50 per gallon.... You'll save 14.28 gallons of fuel and if it's $4.50 a gallon... That works out to $64.28 savings, for every 100 gallons you run through the truck...... It seems like it beyond time to start caring about mileage!!

threemen gets as good of mileage with his IH 4400 (300-330 horsepower, 800-950 ft. pounds of torque!!) as I do with my one ton gasser....pulling less weight!

Hate to say it, but that is running too fast with that mileage too.  it will get that running 80.

Thank you for the information. One of the reasons that I had considered moving up is due to braking. I think that I will investigate alternative braking solutions ie. exhaust brakes.

Thx