Get the 330i. The extra power is well worth the disadvantage in winter. For the snow just get another set of wheels on some good high perfermance winter tires and you're set.
As for your concerns about the ride quality, go and test drive it for yourself. The E46 SP rides way too softly for some of us here, but some buyers complain that they can't drink their coffees while they're driving without spilling it. It's all subjective.