I've had them on and been wheeling them since last July - sat @ 5" when I installed - now they're at 4" when the back is loaded up with 250 pounds of tire and tools with full tank.
I've had mine for over 3 years and they ride great. They sagged maybe 1/2" to 3/4" in that time. No idea how much lift they give as I'm running 1.25" lift shackles and 3/4" blocks with them.
I'm not sure how much lift I got with mine but it hasn't settled very much and I've had mine for a year.And I sometimes load mine pretty heavy with bags of top soil and stuff like that.