AWD car with winter tires... Doubt you'll notice any snow performance issues between the two...
You may notice better dry road performance with the 17" set-up, though... plus, the car will look better..
I've run the 17" set-up on three different RWD E46s.... and, they are all tanks with winter tires.. nothing can stop them... Take the best deal and run with it..
2006 330Ci ZHP Imola Red
2011 X3 Bluewater
1987 325iS Bronzit (retired)
2011 Z4 Space Gray (retired)
2008 X3 Sapphire Black (retired)
2005 330Cic Silver-Gray (retired)
2003 325i Sport Steel Blue (retired)
1967 2000CS Delphin Gray (retired)