Well, in a 4x8 space you could use all three. I would use 2000 Watts in that space if it is all used for flowering. It would be more then needed (600-400 more then I think is needed) but, it will optimize the situation. On one side use the lights you have and on the other, throw in the 1000HPS. It will be a great experiment to see which 4x4 square yields the most/best. Use one oversized fan to cool them both in series and you are a scrog and 3 months from way more then one man could ever need.

The best lights i have are dual spectrum 600hps/400mh air cooled hoods and i have used 2 over a space exactly the same as this.