I used a nova extreme pro on a 180, also 24", (12 bulbs T5HO) and had acros close to the top, they did okay, I wouldn't say they flourished, have them under HQI's and now and they are doing much better.
i have a nova extreme pro 6 bulb and a nova extreme 4 bulb on a 120 gal(48x24x24) and still observing how my corals would react. used to have a 150 outer orbit halide w/ 4 t5 supplement and would say its sufficient for my old 75 gal. but the heat is too much during the summer so i switch to t5 when i upgraded to a 120. I've heard a lot of good feedback with an ati and read that 8 bulb is sufficient for a 120 gal. If i have the money i would go for an ati 10 bulb..