Glad to hear the surgeon had some answers for you.
The jump from 650 to to 1050 isn’t that massive, the extra 400 is approximately 60% of what you have now.
If your skin is currently very tight over your 650s then you need to rethink going larger or wait until they soften up.
You don’t mention how long you’ve had your 650s or if you had problems with them.
So if your surgeon is saying he can and you have seen pics of his other patients and they look good then it sounds possible.
In my experience, a lot of surgeons are conservative, they do not want to risk their reputations or insurance rates by stepping outside of a very safe zone. Even if that means not giving a patient what is really possible or what they want.
With size comes weight of course and you’ will have more than a Kg in each boob. So consider looking after yourself for the first 3 to 6 months after the surgery with good bras and no strenuous exercise or lifting, so they don’t sag , bottom out or other problems
Look at Linda Steele as an example of bottoming out, and give yourself time to properly recover so they can heal as they should.
I’ve seen boob jobs ruined because the girl goes back to the gym to soon or does not wear a support bra,
Then it’s surgeons fault for poor skills or the size of the implant is blamed for being too big as it’s outside of the safe range that the conservative surgeons recommended.
Hope you get what you want and it goes well for you.