This comes down to a bunch of questions about how you use your truck and how much more modifying you're willing to do. You really have to be prepared to mess with brakelines, shocks, driveshafts, steering correction, etc all over again. Some of this may have been adequately addressed with your 4" lift but it all needs to be considered. The driveshaft angle is kind of a big one here. With a 6" lift, you'll have a hard time getting away without a CV joint. With the 4", it can be done in some cases.
Doing the 1" body lift is a good way to pick up some clearance without messing up very much other stuff. I'd say you should strongly consider what a 5" lift will do for you, it's a lot easier and cheaper.