My room's pretty much exactly that size and I'm running two 42W 2700K CFL's and two 55W 6400K CFL's. Pretty decent results but honestly I would go bigger if I had the funds. 400W maybe even 600W HPS, keep in mind this would be for big yields only not of necessity.
Yea honestly I say the 400 watt at 100% but it has to be air cooled. I mean lets be honest, 2.8ftx2.8ftx 5 ft and the dimensions of IMO a small hood like apollos is
Dimension: 24" x 17" x 9" Air Duct: 6"
This means we only have enough room for ducting on both sides of light and at the max, with light distance from top taken into consideration, 2.ft vertical height from the bottom of the tent to the maxed out point.
My suggestion, squat pots, one maybe two plants, topped early, scrogged, something that bushes out hard like white rhino.