I play around with 5, 7, and 10 gallon pots. I'm in coco though. Definite difference in veg time and yield. I've settled more on 5 gallon now since I'm only running my 4x2 for awhile due to a recent move, and they just take up less floor space. Not sure exactly how it applies to soil as I mostly only grow photos in soil, outside mostly, when I feel the need to do that.
I have a friend that I helped get into autos and floraflex nutes. He recently switched to autopots. 5 gallon pots and coco and on only his second grow ever, he got results that rivaled mine. I get good yields, but I'm too much of a control freak, I think, to use them.