But AI certainly wouldn't certify you for TO with a temperature that is too hot for a RTO. Therefore, if you TO with 300°, AI must have made sure that you can safely absorb all brake energy in case of rejection.
That's an assumption. Pantload is correct - I asked the same Q of our Tech Dept. For performance purposes, a lot of other assumptions are made by AI, some of which we are not informed about. They are not always worst case, since the resulting performance figures would be too conservative to be practical. For an RTO, the brakes are assumed to be 150C.
There are always a great may factors which may affect your ability to RTO safely from close to V1. Taking off with high brake temperatures limits the amount of energy they brakes can absorb. Why introduce another risk factor into an already risky situation?
Brake Fans are there for a reason. Don't like the noise? Buy some ear defenders!