2 gallon is fine, you will just find yourself having to water a little more near the last 3-4 weeks. i hear rumors of 2-3 ounces out of a bagseeded 2 gal girl.

people have harvested non root bound 2 galloners... of course they didn't veg too long.

some use the size of the container to control size as well.

i will definitely agree with, more is better, but that assumes you have the space, and that, honestly, your setup will be optimized with larger containers, and plants.