Myself I am using the 430 Watt Philips Son Agro HPS bulbs. I like them very much. I can grow tall Phrags and one lone Vanda under the 430 W lamps and I get good blooming every year. One lamp would do well for your 5 x 6 area.
Now is the electric bill is a concern, and you have a little extra capital to get started - in Alaska - where even greenhouses have to supplement light in winter - I would try LED lights. I visited 2 growers who were using LED and the results were pretty good. The color of the lights is disturbing, so I would not use this system in your living room, but 5 Watts of LED puts out a tremendous amount of light. The Alaska growers got their lamps from
http://www.ledgrowlights.com/
I think if I were to switch to LED - I would have some compact fluorescents or ordinary cool white fluorescent tubes around to provide a little natural light so you can see what is going on. If the only lights you see your plants in is the red & blue of the LED the effect is tough on the eyes as you get confusing color cues to the eye. A little full spectrum light in the grow area will make the human feel better. I am not expanding my grow area, so it may be a while before I try these, but my electric bill keeps going up, as lamps age, I am thinking about trying something new.
One note of warning from my Alaska people: surge protectors, as in the UPS-CS type units for computers that use a battery to condition and smooth the power from line voltage, are suggested for LED lamps, they have a tendancy to fail after a power company does a brown out or power failure and the associated current spikes when brought back up.
For what ever it is worth, my 2 cents