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The driver and their skill level.
Aside from that, yes every car will be different and some are faster than others, although the difference will likely be negligible. There can be a lot of different factors, but mostly it's just due to variance in production. BMW does not intentionally make the newer model year any faster than the previous as long as they are the same model and package. A standard M5 will not be as fast as a M5 Comp, but same to same the difference will likely only be noticed when you factor in the drivers ability in the car.
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