I have a 42" extension and tow a 7x14 enclosed V-nose trailer (all aluminum so light curb weight) with bikes. Two HD bikes would weigh a bunch more but I'd still do it. Curb weight of my trailer is 1800 lbs and I've pulled it with 2 550 lb sleds in it. I will not tow my 23' boat with the camper on though, that is 7500 lbs and the tongue would simply be way too heavy.
01 Red Chevy 3500 CC 4x4 Duramax: Super Hitch, Tork Lift tie downs, Firestone Air Bags, Rancho 9000x, Hidden Hitch front receiver, Peragon Bed cover, Westin step bars - 03 Arctic Fox 1150