Training will be your best friend for big yields, aswell as a good seed bank and good genetics. You can check the breeders info on their strains to see which one is the highest yielding. But yeah, there really isnt a good way to determine how much youll get from a plant, theres just too many variables. If you want the highest yields possible look into some XXL strains which are more sativa dominant, and if that isnt enough then maybe look into photoperiods.