I think some growers often overlook an important point: CMH may be more the efficient bulb with more PAR/watts, but its output is spread over a wider spectrum than HPS, which has most of its output concentrated in the yellow-red spectrum - right where the plant wants to flower.
It's why HPS has been the standard for so long - because in real-world flowering conditions, it's still hard to beat. Once you turn that HPS bulb vertical and start using its entire 360-degree output, it's even harder to beat.
I'm sure a double (630w) CMH vertical grow would beat a single 600w HPS, but there's no way a single 315w CMH is going to rival a 600w HPS when it comes to straight-up flowering. And I haven't even compared CMH to DE HPS when both are operating under a hood, either.
Then there's the start-up cost . . . Again, HPS is hard to beat for a small home grow when you're on a budget , because a ballast and bulb can be had cheap and you don't even need a reflector - just hang the bloody thing vertically from the ceiling and put all your plants around it.
If I sound like a bit of a HPS fan-boi, it's only because I've seen the real-world results. It ain't dead yet.