I keep seeing people fucking up the same way with COBs. You guys are putting waaaaaaaay too many over a small area, you really need to space them out more, there's a lot of light that isn't being used efficiently. People putting lenses and stuff on them to tighten the beam angle, reflectors, all of it. Don't do that. Why COBs are so good: here it is. Cross-lighting. You want as much wash-over from one LED to overlap with it's neighbors. That way, you just have an omnidirectional field of light, nothing in the tent will cast a shadow because it's being evenly illuminated from every angle. This is how you get massive yields, skinny, tall, and defoliated plants that will get even penetration all the way down. I think COB really only starts to shine so brilliantly in a 4*8, but they do work well in smaller tents. I think 4 CXB3590s is plenty for the space, maybe even 3.
There is no way to use HID lighting and grow quality cannabis in a space that small. Not practically. Most LED is not going to cut it either, you should look into this company:
http://www.pacificlightconcepts.com/
It's pretty much the first commercial unit that uses the same driver and chips as the DIY guys. A good option though.