2 150w or 1 250w HPS?

Hey, im getting a new grow tent that is 2.7x2.7x5.11feet tall and was wondering if i should get two 150w hps's or 1 250 hps? I would also like to know how much a 250w hps costs? If i do choose that, i would want an "air cooled" reflector...not sure about the ballast or anything..so if anyone could give me a rough estimation of what the cost for everything need for a 250w hps. And also, tell me what you think i should buy, the 2 150w or 1 250....the 150's have built in ballasts and no air cooled hoods so im a little worried about heat from them..but i am getting good ventilation..thanks

I personally faced a similar question when designing my flowering cabinet of similar dimensions (2.5'x3'x5). I went with the 250w in the end mainly because light diminishes exponentially with distance so while the 2x150w lights would be great in a SOG type setup where you were growing several short plants. But in a box that size I wanted to make sure the few plants I have in there bloom evenly.

In terms of cost, most hydro lighting in my area runs about $1 per watt so my 250w (Bulb, controllable ballast and reflector) was around $250. In terms of heat and venting all I have is a fan at light level and one at ground level with the ventilation out through an inline duct fan. This seems to keep temps. optimal right now in the winter, but I may have to add more cooling for the summer months.

Hope that helps.