I'm in Vancouver so essentially the same climate as the pnw.
I think if you had an m3/m4, you might as well throw on winters. Your pss summers are probably not a good idea. Besides, if you get into an accident due snow (or even really cold weather) you run the risk ofinsurance not covering you adequately or at all due to not having proper tires.
If I were you, I'd buy winters for the stock wheels, and them get some aftermarket wheels for the pss
(or if you love the stock wheels, you can simply buy a cheaper winter wheel and winter tires) .
Just my opinion.