Need opinion on HPS/MH wattage

I'm all set to start my freezer box SCRoG grow.Interior size: 2ft wide x 3ft. deep x 5ft high (.6m x .9m x 1.5m) or 30 cubic ft.(.84 cu.meters) Electrical all set up, 3 plants (NL), 6" exhaust with inline DIY carbon filter and adequate passive air intake. etc, etc. I am questioning myself on the light /wattage size 250watt HPS/MH or 400watt HPS/MH ????????? I'm also concerned about the heat/temp differential and all that, just asking what the experts think on light wattage size that will work best in this space. So far I have a 50%-50% from my brothers from other mothers.