Late to the party, but I have a 2011 G37xS as well, I ended up going with this set up; my main concern was the wheels not fitting over the brakes, but I've been told this will be just fine.

Wheels - Fast Wheels Samba 18x8
Tires - Michelin X-Ice 3 225/50/18

First winter with the car, so we'll see how this goes.