Bud,
I think the limiting design factor for LED Arrays should be watts per square foot of grow. The whole point of spending all this time and money is to use less electrical power to get an equal to a higher power HID.

I have limited my designs to a max of 35 watts per square foot. I would say most HID users are at 50 to 60 watts per square foot. I feel getting even a 30% power reduction would be highly significant and well worth the extra $$$.