I think four bulbs is plenty for a 55. I'd even go with a 36" fixture, you'll get just as much par on the side panels with a 36" wide as you will with a 48". You just won't have to clean the side glass as often.
I'm planning to upgrade my 15g nano to a 40g 36x15x18 I plan to use a 4 bulb t5 fixture with some led strip lights front and back to add some shimmer. It will be a mixed reef with sps and lps.
Also honestly the fixture doesn't mean crap, you are led to believe this reflector or this and that. If you look at Glennf of dsr who has one of the most successful and stunning reef tanks out there he makes his own reflectors from some kind of aluminum foil. Cheap simple and again a stunning long lasting reef tank with spa growing so quick.
The only I would say is find a fixture that has two power cords so you can control the lighting that little bit better.
Here in Australia our standards for tank size vary so much. There's a few basics but I assume vary much more than you guys. I've always wonder how you guys say this many gallon and everyone knows the dimensions haha.
Also I just googled the fixture you suggested and I don't see why not. Think about it this way a fixture only powers the bulb and keeps it in place that is literally it. Ofcourse a few things can come into play heat distribution and reflectors but as I mentioned above if a well known highly successful reefer makes his own reflectors from cheap aluminum I'm beginning to wonder about if fancy reflectors are really all their cracked up to be.
Does it have 2 power cords though? Not a necessity but nice to have.