If you *can* brake during the turn, you didn't have to. To put it another way, if you are going so fast that you absolutely have to brake during the turn, then you have no choice but to give up on making the corner, set the bike upright and straight, and panic brake while you ride off the corner like the polka-dot guy did in TdF05. You only have so much traction to spend, you can either spend it on braking, or turning, but not both.