My comfort level would be about 1000 fpm. Johnson Creek, though wouldn't be too much of a challenge as the runway for takeoff runs down stream. Meaning there is a river that parallels the runway and it runs down the fairly wide canyon and a left turn following the river down the canyon is a typical departure. Other strips would be different as they all have their own challenges - or not. When our group flew the back country 10 or so years ago we all had a copy of "Fly Idaho" a pilots guide to the more remote strips. It has a rating system from easiest to most difficult. I checked and our edition is long gone, but the 3rd edition is available.