Stevie, I know that the RD60 will outrun an MB5, and since the 50 is a whopping 4cc smaller (so much for truth in advertising), it should be dead level with the MB. The RD will also leave the AR50 for dead. Now against such powerhouses as the NS50 or DT50LC, the little RD will hold it"s own but will be bringing up the rear. I raced my first RD60 in a YSR & mini GP class and whupped "em all - might have been the rider, but I doubt it.