We too went from 4 ounce to 8 ounce bottles (first the Playtex dropins, then i realized i want glass so bought evenflo glass bottles - which i LOVE and are very cheap at target.com). They sometimes take in 7 ounces in the first feed in the morning, but otherwise they usually stop by 6 ounces.
Re: 6oz bottles - how long do they use them?
Baby #3 due September 12, 2014!