I use a 1000w in an area like that, I would think about 2 400's if you are willing to take the time to work out your ventalation, and I would think about a Eb and Flow table with that hight. I would look at a 2x4 table if you could fit it in there. I think you could get about 8 to 12 in there if you veged for less than 3 weeks and get about 1.5 to 2 oz per plant once you dialed everything in and if you used the 2 400's or a 600.
Also, with lights that are 250w and higher you really need an inline fan and not a computer fan. In mine I have a 172 CFM Vortex, 2x90CFM Daytons and a 280 CFM Squirral cage, but I wouldn't need that much if I used a 600w or 2x400's..
Adieu