Last week I climbed for 37min at about 3.8W/kg with a 34/23 on a hill with an average grade of around 6.5%. My average cadence was 85. I'd prefer to be a little higher but was in my lowest gear. If I were to climb a 7% hill at 3W/kg I would need a 31 tooth sprocket to maintain the same cadence.

The climb I did was ranked 411/4200. Someone with 3W/kg would take 47 min (3.8/3 * 37min) for the same climb which would be good for 1945/4200. My conclusion is that more than 50% of the riders going up that mountain could use a rear cog of 29 or more.