I have AWD, but as soon as the temp drops below 45F my MPG plummets by about 4 mpg, even when driving steady-state on the highway. I keep my tire pressure around 38psi. In the summer my gauge reads 33+(actual 31ish) and in the winter I'm lucky if it's over 27 or 28(gauge and actualy). When it dropped into the negatives(in F) I had a few weeks of 25mpg averages. That's probably more for warmup time and the fact that I'm still running all-season tires instead of tires with winter compounds.
By next winter I will have a grille shutter system for this puppy. Every bit counts!