Towing with a 2009 Ford F350 6.8 V10 4.10 Supercap LB

I think you should upgrade your trailer to the larger model you want and be happy. Your truck will handle the trailer just fine and you can then decide if you wish to change gears. Personally I would stick with the 4.10's to have a better solo driving truck and I doubt the difference in towing performance will be worth the expense.