Do I Have to Rev Match When Downshifting?

When you do downshift (without coming to a complete stop) it's important to "rev-match." This means raising the engine's rpm as you release the clutch to more closely match your vehicle's engine speed to the rear-wheel speed. Again, this is only important on downshifting.

Is it bad to downshift without rev matching?

Rev-matching is a technique used to downshift gears on a motorcycle. ... When you downshift on a motorcycle, the engine RPMs increase. If you do it without rev-matching, the engine will feel bogged down and the motorcycle will also lurch forward. This can be avoided by simply rev-matching while downshifting.

Is it bad to over rev when downshifting?

Don't think it's going to matter as both will be trying to adjust speed, suddenly, and tires will lose some traction either way. But you never want to over-rev on a downshift. Get as close as you can, and avoid downshifting to red line until you can to the rest perfectly than ease toward red-line.