I'm on the flat east coast so barely ever run into any hills. Around here it's flat as Kansas.My biggest critique of the ACC on the CX-5 is the overzealous desire to maintain the speed no matter what. It only tends to give a ~1-2 MPH buffer when coasting down hill before braking down to the set MPH.
It kills your top end mpgs when it brakes down every single hill. Otherwise, it's so handy on the interstate.
If I were dealing with a lot of hills I would probably just turn it off and drive with my foot.