fAs ar as mileage and for mountain usage I would strongly recommend you get a manual transmission.
Manual Transmission allows for much better control of shifting as you ascend in the mountains for improved power.
I've owned all manuals before the Outback and our Sienna, but the Outback has a manual mode for shifting so you can still downshift manally when in the mountains. A CVT is not the same as an automatic transmission, it's more like having a 1000 speed. Manuals used to get better mileage than automatic, but no manual transmission I know of can equal the mileage of a CVT on the same vehilcle (regardless of make). A CVT should always get better mileage and you can change to manual mode when ever you need to (espcially when going down-hill). Going downhill for engine breaking is usually the only time you need the manual mode because the CVT constanty changes to optimize power. Here is how a CVT works:
The Forester is currently rated 21/27 for the manual (no CVT available) and the Outback 24/30 (for the CVT). I've been getting better mileage with my Outback, but it's two years old now (2011).
You are absolutely right on the ground clearance for the 2013's though, though Subaru does say "up to 8.9 inches" for the 2013 Forester and a straight "8.7 inches" for the Outback. I think even when I had them, on paper they were equal, but the Forester exhaust pipe hung lower. They probably vary slightly year to year though.
As said, I recently had both and rate both highly, but to me the Outback has more advantages (except for price, acceleration). A Forester isn't bad though and is still a good vehicle and one that I was very pleased with.