I'm about to put 2 new fronts on... I've been finding deals on craigslist the last few times so I'm gonna stick try that again.

As far as a bigger tire getting more milage...remeber it's always a trade off. Save here- loose there..

A taller tire is better on the highway (less rpms) but worse in the city, harder to start rolling. If you do all highway a taller tire might have you see a benefit. If mostly city, a shorter tire might show a savings, but will ding you whenever your on the highway.