Lighting question 250 or 400 hps

I have a small grow area (LxWxH) 4x1x4. My main concern is keeping my temps at 80 or below, this will be a chore.
It has been explained to me that for every 1 degree above 80 you Lose 10% yeild.
84 degree's = 40% loss due to heat.
It was suggested to me that if heat were an issue I would be better off using a 250 hps vs the 400, Less heat but better yield. Any thoughts or suggestions on this?

Also, do you have a preference on which 250w or 400w Ballast. Lumatek vs Galaxy vs BGH

How many plants do you intend to grow in that space? If heat is a problem, vent it.

Will have 6 plants total.

go with a 400 thats what i use just make sure you can adequately vent the heat.

As far as your heat to yield ratio that makes no sense to me if where 90 degrees (still not enough to seriously hurt the plant) then you would lose 100 percent of your yield according to your chart.