Given you'd end up on the wrong side of a huge mountain, we descended on the same side we ascendedI imagine those are very short bits, like around corners? Damn, that must be killing after a long steep climb. We did once do the Muur van Geraardsbergen at the end of a day once, which is average 9,1% peaking at 20%, on cobblestones (and not neat ones like on the Gotthard pass, we're in Flanders after all). The only good thing is that it's very short. The name translates to 'The wall' for a reason Actually the biggest problem there was that I was in an extremely low gear, and the cobblestones give hardly any grip, so it was very easy to slip your back wheel.
I know what you mean, one of the hardes climb I did in one rush was this one. You see there is a 17% and a 20% part near the end.
But as you can see, this one isn't nearly as bad. Some steep bits, but mostly it's doable, just long. But gorgeous views, and because you have the tunnel and the main road, the small road is practically deserted which is very nice. It's the only big climb I've done in the Alps, are the rest as nice to do on your bike?