We have some pretty tough 1/2 mile climbs here, but nothing over about 15% or so that I know about. Further north we do have Brasstown Bald which has a 1/3 mile section that is said to be over 20%. I had to walk Ribby up it in 2006 when the 30/28 low gear on my Campy triple wasn't low enough. I came back a year later and barely managed to make it with the same crank with a MTB derailleur and a 13-34 freewheel for a 30/34 combo.