I personally dont see how trying to kill the plant by over feeding could make it produce more. Seems completely backwards to me.
Until someone runs some side by side grows with clones from the same plant, and all other factors held exactly the same, Im gong to consider this stoner science 
By the way - GPW is 100% useless as a metric for deciding how good/bad your grow is. It tells you nothing.
If you want great GPW numbers, just veg longer. A longer veg cycle will give you larger plants, and that will inflate your GPW number. People who grow with short veg cycles will always have lower GPW numbers and those who veg until they have trees will always have better GPW numbers.
Those differences have nothing to do with the lights or the watts.
For personal growers like most of us, grams per day is a much better way to compare results. I dont give a gives a crap about what lights are used or what the wattage is or how long you veg. All that matters is how much did you yield at the end and how long did it take. More yield in less time is good. Less yield in more time is bad.
K.I.S.S. 
P.S. I am conducting a personal campaign to kill off the use of GPW as stoner science 