i would personally bet that its totally dependant on the strain. iam using 1ltr bottles cut in half to start in. this way i can see the roots and how far along they are progressing. these ones i have going now (BlackJack) are forming roots at a slower rate than my previous bagseed sativas did, and they are now starting week 3 in the same container. they probably would have been transplanted around now (5 nodes each, about 3" tall) but i topped them, and knowing this was gunna stunt for another week, i left em for now. once i see some signs of REAL growth again (iam already seeing small signs but its not racing like it was before) ill transplant.
as the threads that have been linked show, a party cup grow is more than possible, but i would bet size, yields, etcetera, would be detirmined on things like strain and nutrients than it would on root growth. ive seen plenty of plants that were high yeilders , and what some would call 'root bound' plants, in small containers, and ive also seen pathetic plants in 5 gallon containers. just my .02