Go with 19's. You don't want those wide tires in the winter.
I picked up a set of Breyton Mesh 19's, with practically new Hankook Ipikes, and TPMS, for $1000.

Just search the typical locations, here, other forums, Craigslist, etc... You have some time.
I found mine on Craigslist.... Guy had them on his X5M for a month, then ended up buying a Cayenne Turbo.