I plateaued at around 7C+ boulder/8b sport for quite a few years in my twenties. Then I made a jump to 8c and then 9a in a surprisingly short period of time. In this episode I go through what I did. Yes it involved a hangboard! I'm not sure my intervention would have the same effect on most climbers these days, but I will suggest some other equally important training for climbing that should reach the same place.