If you ever get 42 grams per watt, I wanna learn your secret. Since that'd get you 37 pounds from a 400 watt light.

My first grow was about like yours: SCroG-in-a-box, 136 grams of bud from a 400 watt light with 240 watts of CFLs as accent lighting. So, 0.21 grams per watt. You get better as you go along, of course, and I learned plenty from that first grow that should enable me to do much much better.

The things I am personally going to try include: doubling pot size (I used 2-gallon pots, trying 4-gallon now), much more extensive pruning to create more bud sites, longer period in vegetative growth, and an additional plant (3 instead of 2). I'm hoping these changes will at least double the output, if not triple or quadruple. I'm actually more interested in quality than quantity, since I don't sell anything, but I am very happy with the quality and see no reason not to at least try to improve on the quantity.