I put on 08 springs but just moved my stock spring hangers forward. I have spent the last couple of years looking for that perfect ride and finally found it. I started with Icon 4.5" lift in front and 5" blocks in rear on my 05. I later added DR 4-link. It was either them or Fabtech at the time. Even though the Icon cost more, I would still go with their 4-link over anybody else's. I feel they are built better and they are longer than the rest. All that said I don't think I would do the 4-link again. With a properly valved suspension, I don't think they are needed. I mention my front suspension because you say you are going with an Icon 4.5". I would look into Carli Suspension. Again I have spent the last couple years looking for that perfect setup. I have Carli spec King Coilovers in front and Carli spec 08+ Deaver full leafs in back with Carli spec King 2.5" reservoir shocks. The Carli 2.5 Pintop kit is the same valving as my Coilovers. The truck rides absolutely amazing both on and offroad, words do not do it justice. The 4.5" Icon looked good but didn't necessarily perform, though it would be better than most.
Since you are asking about the rears, mine has seen any transformations. Ride was horrible with stock springs and blocks. Early last year I put in the 08 springs. The ride was definitly better but I wanted to try the Carli 6 leaf mini pack the replaced the bottom overloads. That was a great ride but I found myself using my truck in the dirt more and knew the full leaf pack would cycle better so went with them. I did lose payload with the full leafs but that didn't matter much because I needed airbags with all the different leaf packs anyways. I remove them when I am not using them, takes less than 10mins. Search Carli in the suspension forum.