That light will be fine if you can dial it down, but at full power it will be putting out way too much light to not have Co2 supplementation and would likely fry the plants. If you ran it at say 70% in flower you could do 4-9 x 3 or 5 gallon soil plants under it, or 9-16 plants in 2 or 3 gallon pots. That part is flexible.. but it will only be good for about a 5x5 area. And yeah 2x
SE5000's would light the entire 6.5x6' space. But now that I think about it they might not fit, 2x
SE3000's would fit and would light up a 6x4' area.
But if you already have that light... I dont want to tell you to send it back. It's just designed to be used in a high output, sealed growroom with Co2 supplementation and air conditioning. It's too powerful to run at full blast in a ventilated grow room. So it's only inefficient in the sense that you can't use it to its fullest potential and it limits you to an awkward footprint for that floorplan.