the luminarc throws a square, so you'll be wasting alot of light over the front and back rather than spreading along the tank, so yeah, i wouldn't put one over a 55 either.
i have 2 on my tank right now if you want to see them, could probably also yank one and take over to your place to see it in action.
as for hooking to your ballast, yeah just cut your old wires. the lumiarc usually comes with a quick disconnect male plug on it, you can either cut that off and directly wire it, or better for a few bucks you can get the female end to wire to your bare wires. here's a pic of the 'pig-tail adapter' as they call it:
http://www.pacificgardensupply.com/products.asp?cat=2
but i'm not sure if it actually does come with the quick disconnect on the wire, since it says 'raw wire'. unless you have an electronic ballast that you plan on mounting on the hood, you definitely want some sort of quick disconnect on it, i'm sure hellolights has a quick disconnect kit in their diy section.
another thing to check is to see if this one has the adjustable or fixed socket. it comes both ways, the adjustable lets you move the bulb in and out to center it, it makes a big difference on really short bulbs. but it's also a pita because the bracket sticks way out the back.
the pfo parallel is a good reflector if you want to throw the light along a long tank rather than a square tank.
