I would like to Over-Veg one of my girls into a MO...

Hello Dubb79, your girls are looking good. I understand your question and i do got the answer for you. I already saw a fellow grower had a good start with recommending a 10 gallon pot, to my opinion thats the max size but its the right one if you want to go big. You need the space you want in buts above the ground also in roots in the ground. Also i strongly recommend you start using silica so you get bigger stems and stronger in any wau possible. Usually u mix it in before adding nutes to your feeding water. I see you already topped them thats very good. You may want to give your girls much stronger lighting and train them by opening them up as much as you can so the light can penetrate to every budside. Try to keep the canopy on an even level and remove the lower canopy that gets less or no light at all. Also you defenitly need good nutrients to back it all up and the perfect enviremental stats. Indoor you need a fan airco, humid and dehumifier that al work perfect. That should do the trick i think. You also need to daily check on your girl to see if shes ok and need some attention in any way. In week 3 of flower its mostly good to do an heavy defoliation. I hope this was an helpfull answer to you my friend. Keep on growing, Peace 👍🏾