Ha I have the same area 4x4x8
I use 2 400W air cooled hoods but no air cooling in the hoods (Yet)
I would use 2 600W but I bought the 400Ws for a perpetual that won't happen for at least another year. Now I regret not buying the 2 600W like I was going to.
I figured 2 tents and 2 400Ws would be enough to keep me high all year long.
Personally I'd never buy a 1000W for a tent period, only 600Ws. If I needed 2000W I'd buy 4 600W 2 hoods and put 2 lights in each hood in my 4x4 area. I'd use a inline to suck all the air out both hoods (Both hoods connected) and it'll regulate temps.
I wouldn't say overkill like people in here, I'd say unnecessary.
The only thing I'd watch out for now, is light burn and temps. 12 inches with 2000Ws over their head might burn them.