So for the winter I ran:
F: 235 40 18
R: 235 45 18

And now I've gone to:
F: 235 40 18
R: 275 35 19

The 18"s were nice in that they were inexpensive and did an alright job cutting through the Ohio snows, but they lacked the grip on normal roads that I was accustomed to and they honestly changed the profile of the rear of the car a great deal. The car just didn't look as good with thin tires back there - made it look oddly proportioned. Now with the 275s it looks mean again, and when you punch the gas in 1st and 2nd it doesn't slip at all. Awesome.