I spent some time reading advice on this site regarding wheel and tire size. I have a 2005 GMC Creb Cab 4X4. This is the setup I went with. It did require a minimum amount of trimming on the front fender but it is not noticable.
I went with ProComp's Xtreme All Terrain in LT305/65R17.That tire is 32.6"s tall and 12.1"s wide. This tire looks agressive and has a 40K mile treadwear warranty.
Xtreme All Terrain
I also bought Procomps Series 6001. It has 4.5"s of back spacing and comes in a chrome finish.
6001 Chrome
I also added the torsion keys to level the truck. It turned out to be a pretty good looking setup and the truck drives like it did with the stock tires.
I just thought I would pass this along to anyone who is trying to figure size and backspacing. I did try 34" and 35" tires. They rubbed the driver's side wheel well towards the cab. It rubbed the steel - no trimming was going to solve that. Oh, and I marked the front with masking tape and just made a quick cut with a box cutter. It took about 5 minutes per side to get it just right.
Greg