depends on what you want to grow sps,lps or softies...
On one of my tanks i have a t5 fixture with 8x54 bulbs...I had this on my 150 gallon tank with sps, lps and softies. I know have MH with my t5 on a different tank. I can tell a big difference with my sps are growth and polyps extending alot more..
I now have my old t5 fixture on my 135 with just lps and softies. And are doing good.