Shackle and leaf spring ?

What is the difference between a boomerang and a longer than stock shackle. Currently i have a stock pack with an addaleaf and an extended shackle. Im at 4.5 of lift. My question is... Does the leaf make the lift or the leaf combined with the longer shackle make the lift? I want to stay at 4.5. If i buy a set of leaf springs for a 4.5 inch lift will running my longer shackles put me higher than i want to be? Deavers and nationals are out of the question for me. They are just too expensive. If i run what i have and get shackle relocator brackets will i get a better ride? Or do i need to go a different route completely. My jeep is only going to be used as a weekend wheeler and im not set on any specific type of wheeling. I have heard bastard packs, s10, ranger, full size chevy, etc. I have no idea where to start. I just have the rc 4.5 lift with the add a leaf for the rear. Just trying to get it a little better.