Note, you DO get better mileage with non-ethanol gasoline, which you can get in some places.
I live at 2400 feet elevation. In this car, and even in my 2010 Camaro SS (which also specifies super), there is just no need (and no point paying extra), as the thinner air makes for an effectively lower compression ratio anyway, and there's only so much spark advance that helps mileage (controlled by the computer). If you're down at sea level, you should use the recommended octane, but do try to get it without ethanol. When I can find it here, it's usually 10c a gallon more than the alky stuff. This might change as the price of corn is at all time highs right now...
For me, at my altitude, 91 seems best, I can skip the 93. But 91 does do better than 87, all things considered.
And you can just leave it in MM going up the hill, all sport mode does is remap the accelerator, it doesn't give any more power with it mashed to the floor than normal or MM does, it just feels easier. And that's easier on the batteries than S mode, since some of the power is coming from the engine - at high speeds, the engine might even be clutched in directly in MM so there's no round trip loss for that fraction of the motive power either.