My 4" lift actually lifted the jeep 5"... But my sprigs were also 14 years of age and started to show a negative arch, so that is really not a fair comaprison (14 YO vs Brand New).
Yes it will. The Extreme duty kit has a little more arch in the springs and will give a little more lift (1/2" maybe). Also, the Xduty kit comes with heavy duty extended shackles which will give another 1/2" or so lift.
YOu can expect a little more than an additional inch overall compared to the Standard duty kit.
I think the kit you are getting is hands down the best SUA lift for YJ's. Taller kits require a heavily arched spring, shorter ones, well they're too short for big meats. A 1" body lift and you could probably clear a set of 33's with that kit, yet still have great articulation and an excellent ride. The next step larger would go to a SOA IMO
Keep us posted and don't forget to post pics of your work and your finished product