if you are going on those 'set' diminsions, you should not go for CFLs. a 400hps would fit in there nicely (given correct ventilation)......if your going for a CFL grow you dont need to make your box as high as 6 feet.....florescent lights do not penetrate that well so you would need to LST and tie down your plants in order for you to use all the available light that comes off of CFLs..
..............if your still set on using CFLs you should look into a Scrog grow, to maximize your light.
" knowledge is not power, knowledge is potential power"
"those who follow the herd step in SHIT"