4x4 can fit 4x 6-8oz plants in but plant numbers are a bit meaningless since you could grow 1 plant to fill that space or 64 plants.
But 315s cover 3x3 ideally. You would want a 630 over 4x4 maybe 5x5 at a push but I have not used a 630 either double bulb or double ended single bulb.
With 2x 315s in separate fixtures a 2m x 1m tent might be best option
I'm currently using 2 315s over my 4x4 planter bed. Seems to work good but doesn't really cover the outer edges of my 5x5 tent, but works great on the 4x4 space.
Well its always nice to have room to move too! Just because you have X size tent doesn't mean you have to fill it.
Sometimes I wish I didn't when it comes to getting in there on harvest day.
yeah so the idea was to use a space inside the 4x8 that would be 6' total. have 2 where the 315 is right above them, and then have maybe 1.5' between the next two and hang the other 315 above that. i feel they need the room. 4x4 is cramped for 5. maybe i just have to mainline to maximize space. 2-3 zips a plant is sad no?