how much are you trying to spend? if i had the money i would go find the cheapest newest gen. mustang GT, get full exhaust, chip, and intake, it cost my friend like 2 grand i think, then i'd get it dyno'd, or go w/ an evo if it was in price range

but that's what i'd do, i love the new mustangs, but you wouldn't see much difference in gas milage though, but a little better