Big he sounds like he is doing fabulously.

My bub was a weeny little one, but SIL has a little boy who at 7 weeks was 7.55kg, and he was averaging 600grams a week, fully BF'd and he is in size 0 as he is quite long as well. They did see a Paed about a week ago and he was not concerned at all. So he is a little smaller, but will probably be pretty close in size by the time 8 weeks hits

He will start to level out with his weight, and moreso when he starts moving, rolling cralwing etc.

You have some fabulous boobie milk

And if you feel too concerned perhaps see your GP or Paed to get confirmation for yourself