I never climb in the big ring. In fact I've always run out of "gears" to shift down to on hills. I just end up with a really low cadence around 50-60 because my legs aren't strong enough to push harder / and keep a faster pace. I basically just end up in Zone 3 for most of the time during the climb on long climbs. I looked back at my longest single climb and it was just over 4000' in just under 3 hours. Out of that entire ride only 1% (1:23) was not in Zone 3 or lower so I figured my legs are too week to maintain a higher cadence.