Go 4 x Gavita 1000 DE,or atleast 3 Gavitas in that space..
i have less height than you and i still suceed to get good numbers,
3lb or more per lamp if you have right strains...
shape your canopy in "stadium" shape... look how in a middle of canopy is like a hole..
there you put plants that have lower strech.. its only 215cm and i grow most of ciclus
on 1150W feature,dont burn plants and have great buds full of terps...
dont belive those folks that say you dont have a ceiling,use your own brain and everything will be alright..
last 2-3 weeks go with dimming on lower wattage..