Just installed mine a couple of weeks ago... what a difference! Went with the 1" to maintain adjustability. I think it is actually a little more than an inch based on the amount of headroom. (believe I saw a posting where the 1" is more like 1.5" to 1.75")
Key to installation is keeping things loose until you get everything in place, then tighten down. I found it easier to mount the rails to the seat and then place in floor... instructions suggest mounting rails to floor first.
Also, had to find longer bolts to mount front to floor. NWE frame rail is a bit thicker and factory bolts were not threaded to the ends (was just catching first couple of the tapered threads and would not tighten down).
Gained more headroom; seem to have lost a little leg room!?! Seat is difficult to push back into last notch on rails due to compartment (floor to back angle) and seat size/shapes. Can also recline the seat a bit more now.