IMO, he's pretty much incapable of being a # 2. But I'd settle - be very happy with it too - if he was a solid # 4, and sometimes acted like a number 3.
Interesting thing about Nick. Looking at his FIP vs ERA you might think he's just getting really lucky. You might even go as far as to think hitters are just swinging at bad pitches and they'll adjust, but Martinez really pounds the strike zone. As of yet, I don't see that there's much for hitters to adjust to.