upsides of letting veg for a lil longer?

2-3 days seems fine to me... You should focus on what the limitations are -- climate, atmospheric co2, light, and space. This is what sets your yield potential relative to the genetic potential. You don't control the latter. You are not going to circumvent 50-70g/sq ft with over-crowding a canopy. Add in genetic variety of seed and it might not even reach 50g/sq ft, lol. A really strong plant might hit 70g/sq ft. An over-crowded space doesn't increase yield. It just spreads out what it can produce given those factors to more bud sites. Too few is a problem to. The happy zone is what you want. It depends a bit on genetics. ~3 colas per sq ft is enough. so, veging beyond that just wastes electricity with no benefit. makes smaller buds result. overcrowds canopy which increases risks of problems etc etc. Even after you flip you have 4 mor weeks of strong vege growth. the plant will double or triple in size after that point, so if it is filling roughly 1/2 th tent, you are good to go. If you have enough leveled out colas in your canopy to fill out with buds, you are good to go. Have a target. Make a plan. Get there systematically to save your effort, time and resources. This doesn't need to be a guess or a gut feeling.