Need advice on T5 setup for 48" tank

[MikeD]

I'm setting up a coral tank that's a 33L. It's about 48" Wide, 12" Width, and 12" Deep.

I was either thinking about going with 6x39watt 36" T5s (powermodule)
or 4 54watt 48" powermodule fixture.

Obviously, the 39" fixture will have less light 6 inches to each side than the 48" model but I thought that may be good for some lower light corals... Also, do you think that 4 bulb vs 6 bulb thing would be a factor? Meaning, would it be better to have 6 bulbs rather than 4 despite it being a shorter fixture?

Any ideas appreciated.

Thanks!

Mike