Well I use a 1000 watt hps on a 6 foot light mover, and I can get up to 8 under my vertizontal reflector without major overcrowding.
But, its still tight.
Worse thing you could do is to cram your plants together.
So, it matters what type of reflector your using.
If your using a wide reflector to disperse the light.
I would say you could grow out 5 with a stationary light.
These are big plants mind you.
If you wanna grow smaller plants, you may be able to fit ten underneath one hood..
It all matters on how your growing em.