As far as I can see it, no matter what your medium is, the more your plants can spread their roots out, the more they will produce above ground. That said, landrace indicas and other extremely indica dominant plants (bubba, etc) seem to produce the best when they have ample time and space to build a massive healthy root ball before flowering, while more sativa dominant plants tend to be able to spread their roots better in early flowering, and don't need the extra veg time or root space; except as nutrient uptake in later flowering may require. I'm just now getting back into soil growing, so I'm no expert there, but I have had plenty of cuts that yielded miserably in 6" rockwool while showing no signs of rootbinding and having by all appearance healthy roots, and then yield double or more when given 2-3 gal. of coco to root around in. Sannie's KO Kush and the Breeders Choice Anesthesia are both like this. It only makes sense to me, as the more roots the plant has, the higher it will come in on the nutrient efficiency/absorbtion scale, and so can absorb more nutes more rapidly than plants with less root space, which would seem to be particularly important in plants that have a short flowering time.
