The metal halides produce a crazy amount of light but also draw alot more electricity and can generate ALOT of heat. With a 250w halide fixture you could grow anything you wanted in that tank. I;m not even sure if the 250w is TOO much light for a system like yours. I am thinking about buying the odyssea 24" 250 halide for my coral tank and was gonna post a thread on it at some point cause I'm not sure if its too much. I have a 150w halide over my 20g now and it seems a tad bit on the weak side if thats possible. lol
Theres also the heat issue, my fixture is beyond too hot to even go near when it's running, I've been burnt by it before. It also raises the temp of my water about 3 degrees. :-( But thats all good cause the tank is open top and doesnt run that hot to begin with. I haven't noticed a surge in my electric bill yet, but I've read that it can cost extra $$ as well.
Also the upkeep on a MH
is a bit more money, the bulb itself can cost over $50. BUT if buying quality T5's they can add up pretty quick too at an average of $20 a bulb.