Breakpoints are matchup specific. There is no such thing as a "general breakpoint". The most relevant breakpoints are probably against Blissey and Regice and Registeel raid bosses. You can check them all using pokebattler but it's a bit of a hassle.
Machamp's highest breakpoint against Blissey is at lvl36.5 with 15 attack. Blaziken is probably lower by a level or a half. Then again, running into perfect def IV level 40 Blisseys might not be that common for you, in which case you're fine with a lower level.