250 Watt or 400 Watt Attic 1st grow

Hello everyone this will be my first post, been doing alot of reading on grow room setup and i want to build a grow room in the attic space i have. Dimensions are 8 ft wide 6 ft. long and 4.5 ft. high. The shape of my grow room is going to be that of a triangle i already have plans for good ventilation (i have plenty of vents i can hook up to) and i plan on insulating the outside walls of the grow room. I want to do a SCROG setup because i only have 4.5 ft. of room to the top. I plan on growing 4 plants in 2 separate rectangular trough pots under the screen with 3 gallons of soil to each plant. The question i have today is about lighting. I was earlier thinking about just a single 400 watt HID for all 4 plants but with only 4.5 ft of space im skeptical if that will be enough room to have it without burning the plants. Now I've read that 250 watt HID could get closer so i was able to find 2 250 watters for about the same as 1 400 watter and I figured the light coverage would be better having 2 lights closer to the 4 plants plus 2 250's is 100 watts more than a 400 watt. Is that more lumen's too?