Most I've gotten was just over 1.50 gpw with a 600 but I don't do hydro or the numbers heath does but with Pro mix and vert setup you will very well break 1 gpw with an HPS I add CO2 I may just get 2 gpw or close to you just stack them and train them right so it fills the space you waste all that good light with reflectors you get much more grow space for a light vertically hung.
I don't care if I convert anyone yall are the ones trying to convert people HPS is tried and true and well known for breaking 1gpw but you don't get more from an LED as I have yet to see over 1 gpw. So please show me something over 1 gpw with your LED's or just go back to being butt hurt about your unwise purchase.