We don't use the same kind of bottles but we moved DS up in size when we noticed he was working hard to finish a bottle and was caving in the nipple.
This. We use Born Free bottles and I moved DD up to Level 2s when she started taking 15+ minutes to finish a bottle, made loud smacking sounds, and would collapse the nipple at almost every feeding. She also had a lot more gas. After we switched her, the gas decreased and she was generally happier. Now she takes only 10 minutes to eat.
Warning
No formatter is installed for the format bbhtml
DS is 5 months tomorrow and feedings are taking pretty long so we keep trying every couple of weeks to move him up to the fast flow for the VentAire bottles but they still seem too fast for him. Milk leaks out of the corner of his mouth. So I think you just have to try it to see.
I just switched yesterday to fast flow nipples on the vent airflow bottles and he seems to be doing well. I think he's spitting up just a bit more but not by much.
Re: When did you move up a nipple size?
This. We use Born Free bottles and I moved DD up to Level 2s when she started taking 15+ minutes to finish a bottle, made loud smacking sounds, and would collapse the nipple at almost every feeding. She also had a lot more gas. After we switched her, the gas decreased and she was generally happier. Now she takes only 10 minutes to eat.