It will likely not take that long to clear customs or security -- in my experience, the lines are pretty reasonable.

I'd head into the city, although you can save at least 1/2 hour in travel time by stopping short of downtown -- the area around the Damen stop (where I live) has many new shops which are honestly too nice for me, plus many places for much better quick food than is available inside ORD.

(The one eatery I'd recommend inside ORD is the Berghoff Café at C-26, especially since its downtown equivalent is closing soon.)