adjustable control arms

I've been looking at RE control arms, and I don't know whether to buy adjustable or fixed arms and I have some questions:

What are the benefits of running adjustables?
Are they worth the extra $?
Will I even need them if I never exceed 5.5 - 6 inches of lift?

I guess I'm asking whether to buy adjustable uppers and lowers, or to just go with the fixed.

Yes
Yes
Yes.

spend the money and get adj., especially if you going to do more lift.

I think it would definitely get adjustable arms at 5.5 to 6 inches. The price difference isn't that much when you consider how many changes the average person does to the height of their jeep. Even if you only change the height with a spacer, the caster can at least be dialed in. Every little bit helps when you start dealing with death wobble.