I love that metal halide shimmer as well. I am far from an expert on lighting but I have done a bit of reading before designing my hood. I think with the depth of your tank that 150w would probably be sufficient to keep most anything. If it was going to be a strictly SPS tank I would say 250 for sure, but the 150 is probably fine. Especially if you get a 10k or 14k bulb. If you went with a higher 20k bulb you may want to consider the 250 because the PAR output is less for the higher color temp bulbs. That said, I dont think it would hurt anything to go with the 250 as long as you can keep it cool. Some of the other more experienced people may have other opinions though.