@ttystikk want to weigh in here?
I know he's been looking at exactly this for a long tme and probably has something to offer...
I will defer to others about the performance of the 315W CMH/LEC. I've heard some people compare them to about 400W of HPS, others say they'll do better if hung and run differently.
I will say that these lamps are all the same tech with very minor differences, and that as such the efficiency and spectrum improvements are due to the ballast they run on. Examples;
860CDM lamps run on either 1000W magnetic ballasts or a very special 920/950W ballast that I've only heard about once and could not buy (and never will, for reasons discussed below). My Kill-a-watt told me the magnetic ballast pushes the same thousand watts into the lamp and uses its usual extra hundred to run itself. I ran mine on single phase 240V power. I suspect there's a way to run these or similar ballasts in such a way that they indeed deliver the expected 860W, perhaps on 208V power. This makes sense because they're industrial lighting products and that's a common voltage in such settings.
@homebrew420 might know more about how magnetic ballasts work on voltages other than 120/240.
All that said, if they deliver the performance they do now while pulling only the wattage they promised, they'd be a decent light. As it is, it's a terrible mismatch between bulb and driver, killing efficiency and thus making these 'garbage' for high performance gardening. They ARE very cheap to get into, but I'd be looking to run a crop or two with them just to save enough for better lighting, not for long term use. Bottom line is HPS is better. It's the ballast...
By contrast, the 315W CMH is driven by a low frequency digital square wave ballast which makes it a third more efficient than anything running on mag. It also sports an agriculture specific design which optimizes spectrum and irradiance, which together with the well matched driver makes them the MOST efficient HID light currently on the market.
It's not the lamp, it's the ballast, and building the lamp specifically for it.
I look forward to seeing how these run in a warehouse setting, the cross lighting does make a difference.
These lamps and the 1150W DE represent the most efficient lighting available... in a bulb. They're good for right about or just a hair over 40%, at least initially. All light bulbs deteriorate with use, it's only a matter of speed.
FWIW, I'm never going to get that big square wave ballast for 860CDM because I was soooo pissed off upon reading my Kill-a-watt that I decided to replace everything with COB LED... on the spot!