I have a 2.5 lift, and just ordered some 285/60/20, which will be installed next week. I went with a 10 ply so I'm curious myself how the ride quality will be from the stock 275/55/20. I'll also be towing a 5500# TT, the reason for going with the E rating.
The cost in a 275/60/20 P or SL rated tire compared with a 285/60/20 E was almost 100 bucks/tire. I'm also running a 20x9 rim with a 0 offset. Your setup is a bit out of my realm though. So sorry, can't speak on that portion.
If you're running a 20x10 rim, I doubt you will regret running a wider tire, as that rim will accommodate a pretty wide one. . You jut have to factor in what you're going to be doing with the wheels. With a 3.5" lift, you can easily run a 35" tire. it's up to you whether or not you want to run a wider tire w/ less sidewall, of a taller tire w/ more sidewall, but thinner.