that's called a 45 long actually.
it depends also what you want to keep in this tank. if i was buying lighting for that tank, i'd probably go with the fixture that will allow me to keep whatever i wanted, just in case.
btw, "moonlighting" is over rated. it has never been proven to promote spawning, and the moonlights in these fixtures are either too bright to be called moonlights, or too dim to see anything with the lights off.
will you have a sand bed in this tank? if so, how deep will it be? you see, the less distance from the lamps to the sand bed, the less light you will need to reach it. you could get away with an individually reflected 4 lamp fixture for a while, but i assure you, this won't be the last fixture you buy. my suggestion would be to buy the right fixture now.
sometimes you can find refurbished "nova extreme pro" fixtures for pennies on the dollar. i would look for a 6 lamp nova pro or perhaps a 6 lamp "tek" fixture from sunlight supply. these are the cheapest fixtures i would go with.
a 48" metal halide fixture would work too.
stick with name brands- current, coralife, and sunlight supply are about the cheapest.