I think the Iwasaki bulbs are available in 250 and 400 watt. I think
they will fire on any MV ballast of appropriate wattage, but I'm not 100% sure about that. I do know they use a MV ballast though. 6500k will give you fast growth, but not much coloration. You could grow them under the 6500 and season them out under 10k or higher to get the color. AFAIK
, the Iwasaki is the only bulb that can be used with a MV ballast.