Absolutely. I used 2 20k 1000's over my previous 400g tank and grew bright SPS out of the water. (That tank is now The Fish Store's display tank and they just picked up a couple 1000 watt lamps from me to go over it.)
Now I run 3x1000's over the new display (1000g) and have 3 extra 1000 watt ballasts and 20k lamps if anyone's interested.