I'm thinking of buying a sleeper sedan. I'm down looking at the above two choices. I would appreciate the pluses and minuses of both cars. I believe the bimmer will be "sportier" due to the 5speed. but reliability and maitenance become issues. It appears the MBZ is more expensive but the "only common" problems are weaking PS pumps. What are the performance spec on the M5? Either car will be rebadged the m to 525 the 500 to a e260.