Optimum gear change point is always after peak power, I cant think of a single exception to that other than where cars make peak power on the limiter so you have no choice.
The reason is that the next gear will offer a mecanical disadvantage, so you need to be past peak power before its going to be quicker in the next gear to carry on accelerating by the time you take the gearing into account.
Just put your torque curve into excel and multiple it by each gear, you'll soon see the optimum change point from each ratio to the next, and it wont be the same typically in every gear.