I do think that the M wheels are ligher than the style oem 215's. Any replica wheel will weigh a lot more. If unsprung weight matters to you then try and get the x6m wheels or keep the factory x5m wheels. BUT do not put replica wheels on the brand new x5m. They will slow you down unless the wheels are lighter than the ones you are taking off, which I highly doubt. It depends on what your prefer.