They will easily fit although either set up will look tucked in the rear so you may want some spacers (at least 12-15mm). I would go 225/40/18 for 18x8 and 235/40/18 for 18x8.5 if you're running a square set-up. I have run the Continental ExtremeContact DWS for almost a year and love them in snow or on dry pavement.
Current: 2015 Audi A6 3.0T
Gone but never forgotten: 2009 E90 LCI M Sport