I had snows on my e92 335i and now on my f10 550xi. Even though i got by fine with the 335i, there is no comparison with the 550xi. It goes thru the snow much easier.
If you live in Canada or northeast USA, the AWD is and will always be much better suited, regardless if you have snow tires on RWD. In the winter time, I don't want to just 'get by' ..I want to have the best setup possible in the winter. Just like Goodyear (or MIchelin(?) use to say "Cause so much is riding on your tires"
In Canada you can only buy the AWD...aside from 2011 when they offered the RWD. For resale in snowy climates, doubt anyone will look at a RWD f10.
Just my 2 cents.
Retired: 2009 e92 335i msport
2006 acura TL
2004 Mazda 6 GT GFX