The optimum RPM at the “average” track is generally around 15400-15800rpm (14800-15500 restricted) at the end of the straight and between 8000-8200 (8200-8500 restricted) rpm at the slowest corner. Depending on the layout of the circuit it may not be always be possible to keep the engine within this RPM range. For example you may find at a circuit that has very tight corners but a long straight may require you to run gearing that causes you to drop below the optimal RPM at the slowest turn and/or possibly run into the limiter at the end of the straight.
The rev limiter engages at 15,800rpm, it is a soft cut limiter and works by retarding the ignition to a point that the engine produces no more power. As it is a soft cut limiter it is not unusual for the engine to rev past the limiter when in a draft or at the end of a long straight when using a high gearing.