You have quite a nice room size of 112 sq. ft., 10 foot ceilings is especially a plus!
Anyway, as far as I understand it goes like this:
400 watt: 5 x 5
600 watt: 6 x 6
1000 watt: 8 x 8
So for a room of your size you'd probably want to invest in either 4 600 watt or 2-3 1000 watt. I prefer more of the lower wattage lights like 4 600's because the coverage is thus overlapped created a more uniform and even light distribution amongst the canopy. The choice is yours though.