I did hill repeat training most of the summer with my club. The hill we used was maybe 1/3 mile at 4.5 %. We would start in whatever combo felt comfortable for the first climb, then do 5 more repeats at 2 cogs higher than the first time. I started off the summer in my granny gear, and by the end of the summer I felt comfortable climbing in my middle ring ( I ride a triple) and one of the middle cogs. Oddly enough I would ride all the way home in my big ring afterward, and didn't even notice the hills that I used to shift down for. Sure my cadence would drop, but there was no struggle involved.