tom,
i agree the mileage won't go down too much, and i think i little higher psi can help offset the add'l resistance of wider tires. honestly, i'm just looking for a little better handling then the (relatively thin) oe 225's offer, particularly at highway speeds.

as far as offroading goes, i don't think these cars are designed for 'serious' offroading. the available torque and bumper angles are fine. even the ground clearance of 7.3" is not too bad. but i remember reading somewhere that there is a weakness in the design of the suspension on these cars for offroading. i can't remember the details, but i'll comeback if i can find the article.