I run 285/55/20 on my 18 Sierra Elevation. I would say no rubbing, but one time backing up at full lock going over a bump I heard a touch.
I run Toyo Open Country C/T's which are a commercial truck version of the A/T's. I noticed at least 1 L/100km (about 2.5mpg) less on hwy.
Up to you and what you need. The Toyo's I have are winter rated and "10 ply". I live in Canada and tow a trailer for work. I also like the more aggressive look, so the mileage drop in no way bothers me.
If I didn't care for the look and lived in a better climate and never went off road, I would definitely have kept the Continentals that came on it. Quieter and better economy.