OK...First, +REPS for some GREAT info!
I will happily defer to your expertise on lighting if you agree to defer to my expertise on math!
It seems to me that, when you look at GPW, you have a different definition than I.
I maintain the value of that measurement is in understanding yield/cost. You seem to equate GPW to yield/PAR without considering cost of the PAR.
Is that correct? If so, what would be that value to you of that measurement?
Why would PAR even be a concern if your yields were sufficient (assuming no sacrifice in quality, of course!)?
And, if that was the case, wouldn't you just throw as much PAR at it as you could afford on your electric bill?
Wait! I said "electric bill"....
If cost of electric is going to be your limitation, than perhaps yield/cost is the better way to look at GPW?