i'm hearing ya...

6x 600w lights,
40 plants, hoping for 2 zones a plant... or 80 zones.

here's my take... its what i would do if i had to estimate a yield.

plant count is somewhat irrelevant, as long as you have the lighted space filled with green..

you are running 3600w total - and i would say after a few grows a grower should be able to hit .5 - 1g/w of HID light used... which means i would say you SHOULD be able to get 1800-3600g...

grams/watt is not the ideal way to rate your garden efficiency - and its almost a pointless measure, but for guessing yields, i think there is something you can get from it... one of the main problems with using grams/watt is that it doesnt take into account the time... if you veged for 3 weeks from clone, thats different from flowering immediately... it also doesnt take into account that you are using soil... and 1 gram/watt is usually done by small closet growers, who use a screen or something. and I know, there are vertical grows that have made it well over 1 g/watt... but thats not important.

so, with no pix - i'd guess your probably in the 64 zone mark... about 4 lbs.. thats at the .5g/watt...

pix are always a surprise tho - if you post up and all your plants are 2'ft tall... i would lower that number... if you post up pix of huge ass colas everywhere, you might go way past 2 zones per plant... no way of telling from your description alone, pix will be key..

and even then, its all still guesses...


peace