When we originally bought COBs, we tested Cree, Bridgelux, and Citizen, and decided that Bridgelux was the best option for running at 80W each, as they get 161lm/W at 2.1A.
We never got around to putting our Citizen COBs online for sale, so we have assembled it now, using one of Growmau5's designs (Though we just flipped two of the Aluminium sections, rather than cutting into it, to preserve structural integrity).
The COBs used here are Citizen 1216 3500Ks, which have an efficiency of 151lm/W at 1.4A, and can handle up to 3.6A. We've used an HLG-320H-C1750B driver, tuned to 300W.
Size is 80x80cm. It's a pretty cool design. You won't see it here again.