I have though I used FFRR 20" rims. It has been a year or so but if I recall correctly the RR rims have increased backspacing which enabled less spacer (only 3/4"). I run a 275/55 R20 Open country Toyo mud terrain. You may find that (or at least a year ago when I did this) there aren't many options for 20" tires. But I can say unequivocally the Toyo is fantastic. With the size I have, I do maintain a lift (adjustable rods) and I do get slight rubbing on the frame arms in the front wheel well at full steering lock, not enough to cause concern. I also carry an ECU bypass setup for airing up the air bags in case I'm off-road and something fails. The truck could not ride home on its' bumpstops with the current tire.
The primary reason I went with the 20" rim at the time was/is that they are cheap and easy to find/replace. I bought 5, in A+ condition for $400 from a fellow on this board. The downside is that you have less rim protection than a comparable 18". I've been okay with this because they are cheap/easy to find and replace, rather than refinish. I've also always liked the shoulder the LR rims have/maintain, they seem to hold the bead better but I've never compared them to the compos. Somebodies wisdom would also state that the truck rolls less side to side around town or handles sharply. But I have nothing to compare that to than the stock 19"s I keep with Blizzaks on them for the winter.
I'm happy with the setup, would only consider Compos if I could not buy the Toyo tires again.