I replace the factory bearings prior to ever running a new engine. For 424, I use the Boca Bearing High Performance bearings (ENK-001HP for the TT) for under $40.00. The factory bearings will start to lose power and slow some after 10 or 15 runs. The HP bearings will last a year or better without a loss in power. The ceramic bearings won't give you any better performance, but will last a little longer than the factory stock, HP or HS bearings.