As far as one COB to do both vegging and flowering, that might be tricky. I have vegged with Cree XML2 4200K and after a few months I decided it is a bit too stretchy for my hybrids. I also have 5000K CXA3590s vegging and that seems to control stretch just right. Another example, I had some seedlings a few inches under a Cree XTE 3200K. Obviously too warm color temp for seedlings, but amazingly they turned away from the light and pointed at the window which was 10 feet away and no sunlight coming through, just bouncing off the snow. But 5000K seems to keep the seedlings attention.
And as far as flowering goes, ever notice how leafy outdoor buds are compared to HPS? I always assumed that it had to do with the spectrum although I don't fully understand it. But time is money and when I have to trim leafy buds it really slows me down. So if we flower with a neutral white will we get leafy buds? Maybe the CMH guys can speak on that.
As far as CXA3070 vs CXA3590, bigger is better as long as you are getting a fair price and a top bin. So when comparing the very best bins of CXA3070 3K (AB) and rare CXA3590 3K (CB), the CXA3590 wins. But if you cannot get the top bin in CXA3590 and step down one bin to BD, the CXA3070 AB beats it just by a little.
There is another thing to consider though, coverage and reflector losses. If your COB is dissipating 40W or more, you most likely NEED a reflector because of the increased distance to canopy. And at 50W the reflector makes a huge difference. The higher you go, the more important the reflector is and the more losses. So the larger COBs do have that disadvantage if you run them harder than the small ones.
