As far as a different 14 probably not worth it. The stock wheels are a very light alloy. They also contribute to the aerodynamic design of the car. Personally I was thinking they make a 185 something 15 Potenza which might allow you to find some different 15 inch alloy wheels. I'm sure this would still cost you a bit in gas mileage, but probably not as much as going to a non LRR tire.