I have a double cab, and you should expect to have 3+ inches of lift depending on the shocks--I found. My 7100's lifted my truck a little more than a conventional shock.
Remember this lift amount is over stock with no extra weight or accessories. I found that my truck has the stance I wish it had everyday with 500 lbs of weight in the back. My experience has shown 8 leaf= 3 inches and 9 leaf= 4 inches, and I here 7 leaf= 2 inches.
The main question to think about is how much weight is going to be in the back all the time? I wish I would have done a weight test on my stock springs before I changed out to see how much it settle with 500 lbs. The stock springs have a overload though and the resistance builds up on it, the deaver is progressive and has no overload (just a lot of leafs), its just a way different animal in how they work, and perform.