i'd go with T5HOs the die hard MH
fans will say MH
but at the end of the day the par rating on a T5 is higher then those of the MH
anyways you cant go wrong with 8 54watt T5s, you can get glow fixtures fairly cheap all you need are 4 daylight bulbs (my recommendation is 10 000k or higher) and 4 actinic bulbs. total wattage of 432 watts giving you 4.32 watts/gallon.
another idea is a DIY LED
fixture Rapid LED Home Page
has kits you can buy that will put out just as much light at about a quarter of the wattage
the whole watts per gallon thing is an old school rule and now means nothing with the new advances in lighting fixtures. what you should be looking at is lumens and PAR