It depends on what type of hills you have. Having run heads all the way from 13', 15', 17.5', 20', 25', and 30', I would not go wider then 20' w/o a FT on the combine if you have anything more than just pretty gently rolling ground. For sure not if you have tires less then the 30.5" big tires. 

Unloading with an auger that is barely long enough is a royal pain too. 

I don't really think the feeder house is built heavy enough for bigger then 20' heads. Had to do some welding and making one of our 1460's heavier at the "curve"  where the feeder house mounts at the yoke in the combine. 

I think more negatives than positives going over 20' on a 1460. My experience running 715's,1460's, 1688, 2166, 2188, and a 2388.