I'd say 3000 lumens per square foot is a *minimum*. I have a 400-watt light with a decent bulb that puts out 55,000 lumens into an area about 1.75 times as large as yours (twice as wide, but not as deep), and the plants would still like more light. (I use another 240 watts of CFLs, in addition to the 400-watt light, during flowering.) If you can handle the heat, a 400-watt light will work in your cab, but I would highly recommend using a cooltube and a good fan, else I predict serious heat problems in your future. Basically, I suspect you're going to have to face a choice: spend more on ventilation, or downgrade your lighting.

I'll show you a pic or two of my cabinet, which is 47" wide x 72" tall x 20" deep. I'm not saying this is the best cabinet ever made (it isn't), but it's semi stealthy, and it's basically odor-free. Perhaps it will give you some ideas. I don't let people in the room when the fan is running (that hum would be suspicious), but I have had people in the room with it off, and they never suspected a thing. The carbon filter is on top of the cabinet, hidden behind books and stuff, and does a very good job of eliminating odor. There's a window AC unit in the same room, which keeps the ambient air temps down, but it also sucks all the moisture from the air too, so I keep some containers filled with water in the cab to reintroduce some humidity into the air. The intakes I use are passive, Doran 8"x8" lightproof darkroom louvres, 'bout $20-$25 each online, and I needed two to provide enough airflow.