T5 Light Spread

[LoJack]

I would think you could get away with the 5 foot unit. That leaves 12 inches on each side. I currently run a 4 foot ATI over a 5 foot tank and my spread is great. I would think you'd be able to get away with 12 inches. You'd have lower par at the corners, but as long as you are smart about coral placement you should be good.

And if you're using LED's as your primary and T5 just as supplemental, you definitely won't have a problem.