I have 2, 175watt 10,00k blueline MH and 2 NO 50/50 flour. I prefer 10,000k over 6500K, the blue light brings out the color in the corals better.
Matt: The 10,000K blueline bulbs have a similar spectrum to some 20,000k bulbs, and I think they are incredibly aesthetic. If they are more blue than you like, you can suppliment with actinic white flourescent bulbs.