Watts are watts... be it actinic or daylight. But, the amount of PAR (photosynthetically available radiation) is quite different between actinic and daylight bulbs and not directly related to watts. PAR is what you want, but can't easily measure without an expensive meter. In general, 10,000K bulbs generate more PAR than an equivalent 14,000K or 20,000K bulb. The 20,000K bulbs produce more PAR than the actinic bulbs.
Actinics will help with some of the coloration of your corals, but that's about it. They are also useful in creating the dawn and dusk effect. Others say they wouldn't go without actinics because they don't want their tank to be so white or yellow looking.
Honestly, we grow softies like crazy with 4x65w PC lighting on our 90g (two 10,000K and two actinics). And, there's considerable growth on our LPS corals, but most of them are 1/2 way up the tank or higher (our 90g is 24" tall). We don't have problems with nuissance algae.
On a 55g, I'd seriously consider getting a 4x54w T5 HO fixture (or retrofit) that has the individual reflectors. We're getting ready to upgrade our lighting to a T5 HO retrofit (5 or 6 bulbs, not sure how many will fit, but I bought enough parts to do 6 if possible) so we can more freely place our corals in the tank.