Lighting efficiency

Have been planning grow for a while and need advice on lighting. closet is 5x2x7.5. Will use closet for all parts of the grow. Starting seeds off with cfl's then switching to Hps. I have a 400 mh, hps setup. Just ordered a cooling reflector for it. Also have a elicent 6" inline fan .Here is my question, If I cool that 400 watter down, will it work in that closet space? Or should I get a 150 watt setup and use less energy and have less heat to worry about. I live in the midwest US. Right now we have our hot summer, so my chosen grow space will need proper cooling. In a few months when the weather changes, so will the temp in the house. Which will create a more favorable environment.
I have been doing an experiment on the temp in the grow area. With no cirulation of any sort or no venting, the closet stays between 78- 80 degrees right now. Of course circulation will change these numbers a bit.
So with all of that being said, What will be the best choice in the long run?

you should stay with the 400 as long as you can keep the temp's down. I got 2 250 hps in a area of 4 feet long 2 feet wide and 4 feet tall and I can keep the temps down in the mid 70's and get great results