250W halides would be my first choice for a tank that deep. If you want a cooler option, then a 6-8 bulb t5 fixture would be good. An ice cap retro would be great because you can go with a 660 ballast and do 4 X t5 bulbs, then do another 660 ballast and add 2 or 4 more bulbs to reach you're desired lighting level. That would give you an option depending on your coral choice.