1 gram per watt is a very good yield not an average yield, ya gotta get everything right every day to get such results. Having said that, i've known folks using co2 to get more. You have to view it as a bench mark, if your not getting that, try harder.
High yields are about constantly monitoring the parameters that affect growth and adjusting those which are bottle necking your system. Start with a high yielding strain, then Monitor>react,Monitor>react,Monitor>react. (im sure you already know this as you seem very knowledgable)
If you can find my pic from years ago in the pic dump thread you will see a 2400w room that harvested a little under 1.8kg with a 45 day bloom cycle, damn close to the 0.5g/month of bloom mark. I learned to grow from an excellent mentor who owned the grow shop i worked for, believe it or not he had never grown a crop of dope himself, only tomatos, lettuce and herbs in his shop displays. He pushed environmental control over magic nutrients, boosters and all the other crap thats available in shops and it worked for me. I can pm you his guide if interested (if i can work out how to use the pm function). Sadly he gave the best advice of any shop in adelaide and his business was out competed by greedy shop owners who grabbed as many $ from customer as possible by selling snake oils.
Can i please see these 1 gram per watt grows if there supposed to be the norm cause if i hit a pound which is 16 ounces with a 600 watter im fuckin stoaked. so 21 ounces from the same light which saying the norm is awsome.
Definatly not saying yas cant pull it off but would like some details as in grow style, medium, strain, temps, veg and flowering time ( importnt cause if ya veging for 20 weeks or so to gethuge plants than fair nuff )......and pics of course..