[slicer]

You are in a predicament there. I would not want to keep the Continentals and I would never mix tires. If it were me, I would sell the Continentals and snag a set of 4 Michelin PSS. Mixing tires is never a good idea because they will perform differently in the same conditions (unpredictable handling). I guess if you put around like a grandma then it won't matter but if that's the case why drive an M3? If I saw a used car with mixed tires I would assume that the owner has cut corners elsewhere in maintaining the car.