Good questions. We completed your order by phone, but I will put this online too for reference.
The Pilot Alpin PA3 that we chose for your package incorporates Michelin's new Helio compound, which gives enhanced wet traction, so those will work well in a winter that has a lot of rain. Like all winter they will be good for snow as well. The Dunlops and Bridgestones would also be good choices.
With regard to information that you may have received from other reps, we are currently working on completing the winter section of our database for this vehicle, and incorporating BMW's recommended size along with the standard sizes that come on the car. The gentleman you spoke with may not have had the new information at hand, so he did the right thing to stick with what was recommended until he knew otherwise.
Running the narrower tires will help your snow traction, while keeping the staggered setup will give better traction when the road is clear. Both are acceptable for the vehicle.
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is available to assist with M3 questions.