Rear
Marchesini 5-spoke aluminum - 12.0 lbs
Brembo 3-spoke aluminum - 13.3 lbs
Front
Marchesini 5-spoke aluminum - 9.2 lbs
Brembo 3-spoke aluminum - 11.5 lbs
When you replace the OEM wheels with lighter magnesium wheels you need decrease rebound damping, and (to much lower degree) compression damping. A lighter wheel has less mass so it can move up and down faster (the system has a higher natural frequency), allowing it to track bumps that a heavier wheel cannot.
These illustrations will help you to understand how damping affects suspension movement after you hit a bump.
When the suspension doesn’t have enough damping, the bike feels unsettled because it takes a number of bounces (oscillations) before the suspension settles back down (reaches equilibrium) after hitting a bump.
When the suspension has too much damping, the bike feels stiff and unyielding because it takes a long time before the suspension recovers from hitting a bump. If you hit a second bump before recovering from a first, the suspension “packs-up” and transmits higher impact forces to the bike and rider, and the wheel has more difficulty tracking pavement irregularities.
This is what you want. A critically-damped suspension system approaches equilibrium as fast as possible without any oscillation, and in the shortest time, after hitting a bump. This is best because it give a rapid recovery without producing either a harsh or bouncy ride, and will gives the best wheel tracking of uneven road surfaces so as to maximize the time in contact with the road. This maximizes tire grip in corners.