back to the engine braking... The higher the RPM, the harder the engine brakes. Of course you do not want to hit the rev limiter... In reality, if you were to downshift to quickly, the tires would squeal. In GT3, i do remember losing traction if I downshift to quickly. In GT4, if you downshift to early, the RPMs bounce off the rev limiter but nothing happens. It is as if it goes into neutral. This of course increases braking distances.