I'm doing 2x250w over my 33gal
haha, go big or go home right?
Its really to give me a tan at the same time.
Generally a normal MH fixture/DE bulb will light about a 2ft (length) area, or so i've read. Personally i'd look at doing 2, but i have seen some quite nice 40+ gal tanks with a center light and rock display and shadows on the side.
How deep is the tank? That might factor into weather or not you go 150 or 250. You'd be able to keep SPS with either, just look at how much of the tank you want to light and if the light will be enough to penetrate to the depth desired. Just some things to think about.
Also factor in the circuts of your house, hehe.
You could probably put together a pretty kickass 1x150w + T5 combo, could work out very nice. 1x150w + 2x39w T5 or something similar. Of course on the other hand 250w + T5 = more light and (generally)you won't have to be as picky with coral placement. In terms of these SPS have to be on the top rock, etc etc.
Personally i'd shoot for the 250w route. If you don't mind retrofitting you can get a 250w fixture for like $10 more then the 150. Not including bulbs of course. Thats what i did. My whole lighting setup cost me like $260 (not including bulbs). For 2x250w.