I was just talking to a speech therapist (who specializes in feeding therapy about this.) My daughter has to go to feeding therapy due to her poor nursing/feeding from the start b/c of her heart defects/failure to thrive. She is almost 13 months old now and uses a slow flow nipple on her bottles and is starting to drink well from open cups! Anyways, the therapist has her own five month old son, and she said she would never use anything but the slow flow nipple or stage one nipples - even for a baby without feeding problems. She said she won't transition to faster flow nipples but to cups. I would just stick with the size 2's - since that's working! (I thought this was interesting b/c I used up to the fast flow nipples with my first daughter.)