I would recommend a 60" fixture actually. As long as it's not right on the surface of the water, there will not be dark spots on the ends although there will be a little less light. You could place Lps or soft corals in the lower light areas. I'd do a 6x80w Tek or ATI fixture. Also, replacing 12 bulbs a year will be $200-300 a year. Replacing 6 would be $120-150 a year. Just something to think about.