I've never driven a 6spd only a 5 but I do like the fact that 4500's are much easier/cheaper to fix and get parts for if the need ever arises. I like how smooth it shifts and have never had a problem with the gear split towing 6000#'s. If I'm racing, I can slam thru the gears really fast. Mine has a new 5th nut and a 13" upgrade will happen soon so neither of those are negatives to me. What I like most is none of the high powered pulling trucks use the 5600, they use a 4500 with an upgraded input, that says a lot.

All things considered I'll never have a 6 speed because the HO's don't respond as well to boxes and the #1 reason: The 5600 is a giant tranny and I don't want to r&r it.