can I just say that I'm not sure if it will help for you to compare babies based on how much they feed - it depends on so many factors: birth weight, weight percentile they are on, any illnesses, teething, sleep, activity to mention a few.
If exclusively ff the comparison is really hard already - for example 5x 7 oz might not be enough for chunky Angus, but 6x 4 oz is plenty for little Emily!
As you are mix feeding I'd say it is pretty impossible to tell how much each child is actually consuming, if you just look at the ounces of ff that will not give you the total intake!
what you need to look at is the weight percentile your child is on - if he stays on that curve or goes up/down slightly he is doing well.
you only need to worry if despite lots of feeds and wet nappies he is dropping percentiles (no weight gain, loosing weight, failure to thrive), but your HV will advise on this.
sorry to "shoot you down", and of course it is fun to compare notes so I hope you get a lot of replies for that reason, but I just wanted to say not to get upset if others have loads more or less.