light has a better penetration rate when emitted from a single source as opposed to a tube.
also the lumen degradation rate increases much more dramatically when the plants are further away from the source of light with cfls.
cfls are good for vege and i prefer a 3/2 ratio of wattage with a hps/MH so for example i use a 600w hps in conjunction with a 400 w MH.
As you said you want to use 250 watts,the quality and weight of smoke that you'll get will disappoint you for the time invested, but ya gotta do what ya gotta do.
I suggest making a very reflective box or small area completely painted white, and ventilate well so you can have the lights close.
But seriously think long and hard on the 400w HPS, it'll be much more worth your time and the price per month between the cfls and hps wouldn't be that dramatic under a 12/12 timeline.
with ballast and fan roughly 6 KWH per day, maybe 20-30 bucks extra a month.
you can compensate buy replacing ALL your incandescent bulbs with cfls and lower fridge temp...
you can do it...