Thanks for your answer. Whenever you answer, it is appreciated :) UTMB route is CCC+TDS with slight changes. My husband had TDS and OCC (OCC is half of CCC), so half of CCC would be half "been there, done that" he hopes :)
The first places that you mentioned near Les Houches he had during TDS but opposite direction :) The race began in Cormayer in Italy and finished via Les Houches in Chaminix. During TDS he had difficulties somewhere around Col de la Plate (Italian French border I think) and after, and most difficult was Le Contamines (near Notredame de la Gorge that you are mentioning, but we see that UTMB and TDS are not completely the same routes in that area).
Anyway, the Col de Balme ( actually area near Trient and Les Flegeres) I think that he had during OCC. OCC start was in Orsieres, in Switzerland. He agrees Trient area was difficult.

CCC begins in Courmayer in Italy, and goes via Switzerland, to Chamonix.