I have a pair of Hankook W300 Ice Bears in 225/35/18 from my old 335i that have hardly any wear on them. Given that they are narrower than stock (235's), what size should I put on the rear? Stock is a 255.

Also, given that pizza cutters get through the snow the best, how skinny can I go on the back?

And finally, is it ok to mix brands front/back with winter tires?

Thanks!