6 tons is fine.
i stole this from another site but i agree with the recommendation.
A common problem i see with the DE fixtures is that people dont have the correct distance from canopy to light fixture. I seemed to find best results with this little reference i made up:
(Distance from canopy to bulb) (Light Spread) (Wattage Output)
(@ 2') (5'x4') (600-660 Watts)
(@ 2.5') (5.5' x 4.5') (660-750 Watts)
(@ 3') ( 6' x 5') (750-825 Watts)
(@ 3.5') (6.5'x5.25') (825-1000 Watts)
(@ 4' ) (7' x 5.5') (1000-1150 Watts)
Ive been messing around with the height differential and best wattage used. also helped determine a realistic canopy spread. This little chart^ isnt saying that you should butt up your spread of light side to side. Gavitas work best with cross lighting so overlapping the spread is definitely recommended. I feel that 3'-4' of canopy height is needed when running at 1000W. IMHO its over kill of light in to tight of light spread. Ive seen negative affects @ 2'-2.5' of canopy height, raising the lights helped, so does training and trellising
run your fixtures side by side not end to end. This utilizes the cross lighting too.