I figured I would inject my .02 cents where you mentioned a 6" suspension and dealer saying you need 4" backspacing in order to run. It is true, at least on my 08 4x4 1500. I couldn't run 17" wheels without a spacer (shudder) The issue is that you will not be able to connect your tie rod ends once the lift is installed. The inside of the wheels would be sitting on there if you could even get them on. Though if you got the spacers, it would work although people really hate the spacers.
My solution was to get 18" wheels and tires.... (I am not really a fan of large rims so I wanted to keep them as small as possible) The tires have about a inch or so clearance for the pillar and that is with 4.5 backspacing. Everything worked out great (once I got truck back) and have not looked back.
Personal preference I would go with the suspension lift, as it is never enough... once you get it leveled or raised enough to clear xxx tires, you will wonder about going to the next size.... (especially if you see others with the larger sizes. My tire size is 35x12.50x18 and I had to trim the plastic piece under the bumper and my tires stick out about a inch or two beyond the fender wells. aside from that it is no problem. 4,000 plus miles on suspension lift and it does not squeak and rides real smooth...