The RE 3.5 kit is gonna give you the same height as the 4 inch kit. most 4 inch kits only give you really anywhere from 3.5 to 4 inches of lift anyway depending on the engine size and if you have a hardtop. some factors of weight on your jeep can play into how much lift you get from any kit. the heavier your jeep, the less height you get, the lighter your jeep, the more lift you'll have. its simple physics!
i hope that helps on your decision. you do get what you pay for in the long run, cough (RE) cough.