Comes down to growing technique. Maybe you were a better grower by the time you switched to CMH? I consistently - and I mean almost each and every grow - pulled 1.3gpw from a 2x600 vertical set-up, hitting almost 1.5gpw on one occasion, and that was in coco (no aero/NFT or other fast-growing hydro), no CO2 and with multi-strains. If I'd been monocropping, it likely would have been 1.5 each grow.
I'm not knocking CMH, because I haven't tried it, but I still can't see how a 315 bulb is going to rival or outperform a 600w bulb. I tried plain MH at one stage, but watt-for-watt, HPS always killed it in flower due to the red spectrum.
I can see how LED can rival horizontal HID grows, but I've seen sophisticated aeroponic/CO2 vertical HPS systems yield 2+gpw. I've yet to see rival figures from any other type of set-up. Maybe vertical CMH would do it . . .
Mate, dunno were you were in the early/mid 80s, but we were paying $120-$150 an oz for good local bush weed, a bit more for imported Thai, and up to $200 for sinsemilla. The bush weed was from Thai seed that came from imported weed that flooded the market in the 70s, and it was so good, we used to call it "trippin gear". $350 an oz 30+ years ago is madness - $500 is just plain crazy! The A$ was about 1:1 with US$ back then, too.
I'm glad I knew a few growers back then!