Hmm, what makes you say the 2.p0op is a better motor (assuming stock)? Mpg wise, I think you'd have a hard time getting "30"mpg just because you have to wring the b**** more when you need to pass or join the highway. Getting that kind of mpg around here would mean no kidding grandma driving most of the time.
Now for aftermarket stuff maybe, just because the 2.0 is a smaller motor physically. People are putting miata cams in their 2.0 + tuning giving over 40hp bump. But other than that I know of a 2.5 and 2.0 both running similiar turbos and same boost target.. that being said, the 2.5 boosts full at 3000rpm (and it's rear mounted). The 2.0 boosts over 450p manifold mounted.