Here is what I use. I have no overheating problems.

4x3 closet with 1000 watt cooltube, pulled by a 200cfm squirrel cage and room is fed with a 150 cfm squirrel cage. Light spread is great. I get a very even canopy. 12 plants in 3 gallons

4x7x4 box with 2 x 1000 watt aircooled lights, fed by a 6" 500cfm inline fan and exhausted (through the hoods) by a 750cfm inline fan. 50 plants (30 in planter box, 20 in 3 gallon pots).

5x5 closet with 2 x 600 Digital HPS aircooled lights. Fed by oscilatting fan and passive intake (plenty for now, it doesnt get above 75 degrees in there), pulled by a 700cfm 8" Vortex fan through both hoods. 30 plants in 3 gallon pots.

5x7x5 box with 1 600 Digital HPS for flowering, 25 plants in 3 gallon pots, and 400 watt MH + T5 Flurescents for 6 mother plants in 3 gallon pots on the other side. Exhausted with 500cfm 6" fan, intake with a fresh air 4" 250cfm fan near window.