Not sure they make the 4" for the JK. Maybe the early model JK's? I just had the dealer install the Stage 3 lift with the Fox reservoir shocks. We got it because the dealership sold it for $2000 including installation. We probably would've gone with a Rubicon express kit had we not gotten the deal on this one. The Fox reservoir shocks look killer though!
So far we haven't had a chance to really test it out. Kit recommends a 33-35" tire, but we have 37" Cooper Discoverers on 17" wheels. There are a few others around here with this setup. As far as performance, I think it would take a lot to benefit from the reservoirs as they are designed for hitting bumps at speed but they're not gonna hurt.