[Tempest]

Since you asked, I would certainly go with 15 X 7 inch wheels over any 14 inch wheel. I think the 15's fill the wheel well better, and you have a greater selection of tires at 15 vs 14.

Also, I don't know if this will be noticeable, but your rpm's will be slightly decreased with a larger tire circumference, so there may be some savings there, and less tire wear. I know these are very marginal advantages, but they do favour the bigger wheel.

Please post pics once you have made your selection.