I think you will have alot of factors to consider into the equation when figuring out how much lift you will get from a set of YJ springs..... weight of the vehicle to include heavy bumpers, winch, ect.... also how many miles are on the donor YJ springs.
I was running a set of 2" lifted Bonz-Eye Samurai springs and switched to YJ 5 pack springs on all four corners. I was actually about 1/4 - 1/2" less lift after swapping to YJ springs. I made a set of 6 pack YJ springs to lift me back up a bit and now I sit about 1" more than I was with the 2" lifted Samurai springs.
Right now I am sitting at 23 3/4" to the bottom of the rockers on 31" tires.