Double,
Yield is one of those things that's so variable that nobody can really give you an idea of what to expect. The grow I'm about to harvest is a perfect example- this strain should yield around 3 oz per plant on a 12 week grow cycle (4 veg, 8 flower) and the plants should be between 4-5 foot tall. Unfortunately I had a spider mite infestation during the first two weeks of flowering when the plants really tend to put on the growth, and I'm going to be harvest plants that are just under 3 ft tall and that yield maybe 1 oz each.
As to your specific question about sog versus a 12+ week grow, your going to see much smaller yields per plant. I haven't personally done sog, but I understand that the yields are no more then 1/2 of what you would get if you grew it to full size. The idea behind this method is to maximize a small space-instead of growing 4 large plants in a closet you grow 10 small ones. Since they stay smaller you can grow more plants in the same area and end up harvesting just as much as you would have from a smaller number of big plants. And since you're cutting a month off the grow cycle you get to harvest more often. The drawback is that you get smaller yields, and you have to water, feed, prune, etc more plants. You also really can't use a lot of the topping techniques, since they require veg time to recover and develop the new branches. That might actually have a lot to do with the difference in yield size, since topping techniques can almost double a plants yield.