on a 55, i think a 4x54 would be enough to keep softies, LPS, a BTA and maybe even some hardy SPS and clams near the surface IF the bulbs are individually reflected. Notsure if the one you mentioned has indv. reflectors or not. At my LFS they have a 75 with a 4x54 indv. reflected and they keep the nicest LPS in there you'll ever see. I know aquactinics and tek lights make good fixtures with indv. reflectors. I may get a tek light for my reef soon too.