You don't know how thick the canopy will be. 1000w for a 5x5 space for coverage, and don't forget penetration! What about dealing with heat? Are u venting the light? Fresh air in and exhaust? Size of plants matters for space. So if ur doing one big plant u need the thousand, but if your doing 6 small to get 2 oz each then go with the six. Remember, plants can double in size during flowering. You could flood that tent with 1000w and one plant. Co2 bag and get 8-10 oz in 3-4 months or do six small for 2-3 and get just as much... I'm expecting 12-16 oz out of my biggest ones, maybe more.. 3 weeks left, colas are big as my arm. Hydro, GH line for nutrients, old school... 8 1000w Lights, 5 gallon buckets, CO2 injection. 18 very happy girls.