Genetics play a role. Free seeds are usually free for a reason. Older stock, good but less than stellar end product, on and on. Doesn't mean they can't be good, but again.... they aren't free because they are hot on the market. Not all auto "breeders" are the same. That $12 bottle of corner store Vodka isn't the same as a 20 year old bottle of Crown just because they are both alcohol. Everyone knows it all here, especially the one's that don't even grow autos. That's my opinion. Experience from my grows and what i see is coco or other hydro mediums will make them veg longer than soil. Topping and training will cause longer veg periods. Obviously looking for strains that say large or 250/300+ grams per plant, Sativa dom plant and s/f1s that will have more vigor and jist grow plain faster and almost no stopping are all things to look for. 3 gal even if coco/hydro won't fill a 4x4. Maybe 3x3 if all else falls into place, but still betring you'll need 5 gal and if soil, well i don't grow that way.