It's funny, but on all the Jeep forums Rough Country kits are considered low end, cheap crap. But I've NEVER heard a single bad thing about them from Ram owners, no matter if it's a SFA, torsion IFS or coil IFS application.
As far as the lift height goes, I agree that most people regret not going higher after spending the money, so you should think about the 6" kit. I'm not a fan of running 37" tires on CVs, but 35s look fine at 6" of height.
Now I went with a 4" kit (Rancho) mainly because I use the bed of my truck heavily, especially when I'm up at my small piece of farm property. The bed as it sits right now is about as high as I can deal with it for loading heavy items, logs or deer during hunting season. I also transport my ATV in the bed often and even with 84" ramps, the angle is severe enough now, it'd be like climbing straight up a wall if I'd had gone higher. So there are some reasons to stick to 4" over 6" for some. Just depends on your intended uses...