Trying to improve my English from C1 to C2, I came across this Stanford's lecture (link). The matter is, I understand circa 80% of the professor's speech.
Is such percentage OK for an Advanced user? I have some familiarity with the related topics (psychology, psychology, psychotherapy in English).
P.S. For some time, I've been burying myself into straight-C2 stuff; therefore, I could lose some confidence.