Just wanted to say I agree totally wth Laura, my DD is on the larger end of the percentiles, and has always been so (once she got over her initial weight loss after birth). She always had a large milk intake, I was still giving her 4 bottles of 8oz per day when she started nursery at 14 months of age, and she kept one bottle of formula going until after she was 2. I appreciate that some people (including some HVs) might have felt that wasn't necessary, but I wanted to follow her in weaning her off the milk, and certainly her solids intake wasn't affected at all.
She always had lovely podgy rolls and folds, certainly at 7 months there were many of these. She was a bottom shuffler, and I often joked with DH that she sat unsupported so early (4 months ish) because her tummy helped to hold her up
but seriously, she is now fast turning into a bean pole with skinny ribs and long legs, with none of those lovely baby told anymore.
To me it just seems likely that your DS is a bigger baby, you're certainly not over feeding him milk. Personally I would up the oz across the feeds until he stops draining the bottles, and perhaps even add back an extra feed if you think he needs it. If you're offering solids after milk then I don't believe he should be able to overeat really at this age.
Hugs honey, follow your mummy instinct, if you think he's hungry feed him a little more. Xx