HPS/MH for a 2.5'x5'x6.5' grow tent

The tent is 2.5'x5'x6.5'. I currently 2 600w MH/HPS lights in the tent both have settings from 200w, ,400w, 600w. How much wattage would be best for this size tent?I do plan to SOG this grow. Strain is Red dragon and I do plan to use Co2

12.5 sqft * 50 watts per sqft = 625 watts (good lighting)
12.5 sqft * 60 watts per sqft = 750 watts (high end for CO2)

The real trick is evenly distributing your wattage. Running two lights at the 400 watt setting with 400 watt bulbs may be a good way to go.

You would be far better getting 2 x 315cmh for that space.
But if you want to use your existing ballasts run them at 400 w each.

Two 600W HPS would be an over kill in a 2.5.x5 tent, you'll run into serious heat issues even if you ran air cooled tubes. On 600W HPS would cover a 2.5x4 area,