Seed and Yield question

Hey All...
A modern newbie here, havent grown anything since the late '70's. Been smoking all that time, just have been living in different states, countries, whatever...Anyway, some q's. First, in my research before going into serious growing, I notice that seeds come with different yield statistics. First, some seeds come with the stats of 450g/m2, is this in a SoG or SCRoG mode or is this per plant. If SoG, how many plants to achieve this type of density/yield? Another stat is one that states 25g per f2 w/ 40wpf, which I translate as 25g per square foot utilizing 40 watts per foot. Now I have seen Ed R. stipulate that the ideal is 60 wpf. or is this me reading this wrong. Appreciate the help...
Thanks :o