The steepest bit on my hill-climb training route is a short pitch of 15% at the top of a 1-mile hill that averages around 8 except for one or two places where you jog over a hundred meters on a flat street to get to the next part of the climb as it's in a super-quiet twisty-road residential area. (RWGPS, at least after the hill-climb rejigger, calls it 11% but it's on several local hill-climb training rides and everyone calls it 15% (and it feels much steeper than other things that RWGPS calls 11%)). "Mount Pisgah"/Giraud Road for anyone else from Boston.
8-10% is where I start to struggle; anything above that gets walked on brevets and when tired, stuff in that range too. (I did a hilly brevet today. I walked a bunch of steep pitches that I could have climbed each individual one if I'd wanted to, but I couldn't have done all of them.)