Black Magic. As JJ said, you want the lowers. And i would seriously look at a set of the type i posted up, as you dont have to half remove them to adjust them, and that can be a serious pain to rotate the diff and get the bolts back in.
On Go-Jeeps site, you will notice the chart below. The upper control arms stay the same length up to 4.5" of lift, but you adjust the length of the lowers after only 2" lift..
Lift...........Lower Control Arms/Upper Control Arms
********Decimal**Fraction**Decimal**Fraction
Stock........15.75.......15 ¾........15.00........15
2”.............15.92.......16............14.88 .... ...15
3”.............16.09.......16............14.92 .... ...15
4”.............16.33.......16 3/8......15.03........15
4.5”..........16.47.......16 ½........15.11........15
5”.............16.62.......16 5/8......15.21........15 ¼
6”.............16.97.......17............15.44 .... ...15 ½
7”.............17.36.......17 3/8......15.74........15 ¾
8”.............17.81.......17 ¾........16.09........16
9”.............18.30.......18 ¼........16.50........16 ½
10”...........18.82.......18 ¾........16.96.........17
See also here:
http://www.jeepforum.com/forum/f11/3...-arms-1307226/
Cheers, and good luck..