whats your electrical look like as of now?
i know ng was only .4db off from a 149 on the tl with 1 memphis 4kw and 1 15" btl. he told me though that his score off the memphis was the exact same as it was with his zx2500.1.
he had to add a third battery before his score went up using the memphis amp. basically what im trying to get at, is you got a 2.5-2.7kw amp keeping up with a 4kw on most systems. a good electrical is ESSENTIAL for that memphis to do what it was meant to do.
btw: i would take the BTL. i own a 15" and it takes 3k daily without breaking a sweat. you gotta keep in mind though, that i dont have experience with the other subs listed though, but i know im happy with the btl so far. also, supposedly the BTL takes the power much better than the MT (another sub i dont have experience with unfortunatly). there is a member by the name of Brien Owens here that used to run 4 mt's and now switched to fully loaded btl's. supposedly they take even more power than the mt's did, and are running A LOT cooler for him as well. can be verified by Megalomaniac, if you want to ask him.