There really is only one reason to run long arms and that's to help restore your suspension geometry when lifted tall enough to start effecting your ride quality adversely. At that height, long arms will also help allow for proper axle travel without the swiping you would see with short arms. The JK factory length arms are way longer than the old TJ and up to 3" of lift, there simply isn't enough change in the geometry to warrant the need for long arms. If you are wanting to stay 3" or less, I would save your money and just stick with a good set of factory length arms.
I was wondering the difference between a 3 inch long arm kit and a 4 or 6 inch besides being taller? Would a 3 inch long arm bind or restrict travel verses a bigger spring and having a 4 inch or 6 inch?
Then throw in the factor in my situation of running coil overs. If I installed to a long arm and kept my Evo coil overs and remained at 3 inches verses increasing my coil preload more for taller height any benefits from 3 inches to 4 or even 6 inches
I'm comparing long arm to long arm