You'll probably be fine with 6"
This is DangerRanger96's truck with 5" of lift (3" spindle, 2" coil spacer) with 32x11.5R15 tires. I'd get 15" wheels as well. 16" wheels don't offer big tires in friendly load ratings for our trucks. You'll probably run into a lot of E rated tires and a few D. Both will ride like crap and wear incorrectly.