When you get upgraded arms IMO I wouldn't buy a fixed arm. Things change and you need the adjustable ones to account for it. If you decide that a 4inch lift is too much and go to a 3 then the arms would need to be adjusted. Same thing if you decided to go higher, Though I would not suggest going any higher on short arms.
The control arms do a couple things when it comes to the suspension. Depending on the set up, But in your case the lowers position the axle squarely under the front of the jeep. The uppers set your caster and pinion angle. The trackbar keeps the axle positioned side to side.
So in reality when you lift your jeep and use the stock arms your wheel base shortens, Moving the frame higher by installing longer springs, moves the frame mount higher which makes the arm more vertical, the key is to keep these as level as possible. Look at a stock setup next time you get a chance and look at how level the arms are, This why people install long arms, moving the mount back allows for less angle on the arm.
Making the arms longer or adjusting them out allows you to help correct this. Best thing to do is get the adjustable and set them so the front tire is center of the wheel well when at ride height, Then set the caster, and hope pinion angle is ok.
