I agree with all that you have said. I know that Jeep and Toyota (for the FJ) quote "ground clearance" as the lowest point of the vehicle to the ground - and for both that is the differential which is what I was thinking of. Agree the underbelly will rise and also agree that it's very beneficial. I think Sal-XK was referring to the 4" lift maintaining a better geometry for the suspension than a simple spacer lift (lots of folks use this one as a reason to go to a 4"). I am not sure if that claim is 100% true, but it makes sense.

Unfortunately this might now take a back seat to a new bumper since I scared mine pretty badly against a tree this weekend. DOH!