Here's my reply for you since I see you've logged off I think you'll be good @ 41W/sq.ft. if I got the math right. My fridge is about that size. If you don't already have the HPS, I'd go with a CMH. For a 150W and below they use a pulse start Metal Halide instead of a HPS like the 250W and 400W. I could see you getting an Oz. or more since you already know how to 'read' plants. Post on my build journal if you want.