We used 130W PC lighting over the 20 gallon and it was enough light to grow some of the easier SPS. Birdsnest and encrusting montipora did just fine. That said, I don't think PC is the best choice for a 55 gallon. I'd go with HO T5 for sure, and I'd stay away from anything Odyssea. As was mentioned, you get what you pay for, and I've rarely seen anything positive said about those fixtures. We now have a 6x 39W Nova Extreme Pro and love it, but you don't have to go for that model. The Nova Extreme is cheaper and would work just as well. With 4 bulbs, you won't be in a position to keep SPS, clams, or anemones, but softies and LPS should do fine.
Just a thought; if you're itching to get started you can always start with a FOWLR and upgrage your lighting later, as long as you choose reef-compatible animals. You can use whatever lighting you already have in the meantime while you're saving your money.
*edit* It was
www.marineandreef.com . Excellent prices and they'll ship the fixture for free if you spend $150. I've never ordered from there, but thought about it before we found our fixture used.