Not sure what certainly constitutes a breakthrough dose, but snorted I have taken it up to about 10 mg, or 15 at the highest. That was the orange tinged freebase which stung and probably didn't absorb ideally.
I personally never went for snorted breakthroughs and never smoked, but injected IM and especially in combinations with other things I have experienced breakthrough experiences. In one session I have went through 100-150 mg that way.
Mixing it snorted with ketamine was really really good!
Anyway I'd expect breakthroughs to maybe start happening often around 20, maybe 25 mg snorted? I get it if you dislike getting an anxiogenic not-quite breakthrough, but be careful and don't just dive in all the way immediately IMO.