If you can deal with any hear related issues with the two 400 watt bulbs being added, then I would say to go with those. Thirty inches is a good way for a bulb to penetrate effectively, so using the 400 is a good choice. Just remember to acclimate your corals to the intense light. Have you thought about running 250 watt hqi's....they are suppossedly pretty equal to the 400 watters. I have two over my 120, and I am really pleased with the light penetration, and the heat.

As far as the xm's go, I personally have yet to see a tank in person with them running. From all of the pictures that I have personally seen, they look entirely too blue for me. I like a good whitish blue light, that seems bright, and all of the pictures of the xm give everything a blue hue that I do not think I will be happy with. Good luck with the lighting, as I really like those cube tanks.


Johnny G.