30 or 10 autos in 8x4x4 room

Hey, so me and a friend are doing a grow, the area we have is 8x4x4, that's a floor plan of 8x4 with the highest point being 4ft, the roof slopes following the actual roof, the sides stand at 2ft tall. The inside is painted flat white, there is 4" intake and 4" extraction, the 600w light is hung from the centre of the room, no reflector just the bulb hanging vertically. The big question is how many could we efficiently grow in that space? my friend is pretty certain that because we can fit 30 pots in that space we should do 30, on the understanding that more is better, my argument is that each plant would only receive 20w therefore produce less. I believe that we should have 10 in there on the assumption they will grow better having more wattage per plant... I know we could increase the light to a 1000w but being in the attic, not too sure about heat signatures from it plus electric costs are always a concern. Any help would be greatly appreciated.
Many thanks
Bondutch.

Your gana drive yourself crazy trying to fit 30 plants in there. I think 10 would be an ok start.

Measure out a 3x3 space . That's all your 600 w effectively covers . If it were me I'd do this . 8 LEDS up there . Cover around a 2ft to 2.5 ft a piece . LEDs run cooler than a hot open bulb 600 ( I hope yours is air cooled.) so look best honest advice is to run 10 autos . Smoke and sell the rest . Upgrade to LEDs . Do it again . You'll do better again and again and start with 10 work your way to 30 .

Just because you can fit 30 pots in the space doesnt even begin to mean you can run 30 plants in there. You apparently dont have much height either if your 4 ft from bottom to top right ? The light needs room to hang and you'll need to stay under a 600 watt by a few more inches and now your height is getting shorter already.
IMHO if all this is correct, your going to have trouble with a lack of height overall. Sounds like a scrog or LST at the least would be in order here to maximize what you have.