I'll throw in a vote for the XM 15k. I just switched from XM 10k last week so i dont know exactly what the bulb is going to burn into. Right now i am running it with one vho actinic (back) and one vho 10k (front) to give a little punch and i am loving it. the corals seem to agree as do the fish. Bonus, it is easier on my eyes. I can look at the tank longer. sometimes my eyes would get sore with the 10k.