I've hit 3.5 per under single ended thousand watt hps . And I'm not a good grower, just overly ocd about canopy management. So I'd imagine 5 is doable with perfect grower, conditions, genetics, everything on point. 1k hps single ended. To be honest mongo, my last run, I did better under the single ended than my double ended fixtures . But I'm working with 9ft ceilings.
With that being said. Dude above claiming these numbers seems like a donkey and I doubt he's getting anywhere close to that. 4x4 raised beds in soil? Sounds like a dope gig, but not 5ps per dope.