Both curl-over and the down of a wave bar can make climbing impossible.
The only non Military
VFR accident I can think of in recent years was a fatal flexwing accident last year. The official report has not been released yet but concensus is that he was caught in the curl over very close to the hill below the summit. Substantial MTW was forecast.
The most severe wave I have experienced was this year south of Newcastle. I estimate in excess of 800fpm although as usual it did not last long.
D.O.