i think the assassin's would have better SQ and can hit just as hard (but i don't have much experience with the L5's).
i've got dual assassin 12's in 3.5ft^3 ported to 32Hz with 400W to each, and i've heard the L5's in the kicker preloaded box with 400W to each and my setup OWNS the kicker box! but i think that box is undersized and tuned real high. they L5's seemed to totally lack SQ and impact, but on some of the longer notes they seemed pretty loud.