[Avodah] B'li Neder

[Cantor Wolberg]

Question - is the reward that one receives for doing the stringency
greater if one takes it on as a requirement vs. saying bli neder?

As I recall, somewhere in Pirkei Avos it says that we don’t know the exact 
reward or punishment for mitzvos or aveiros. That’s only known by HQBH.
However, I also remember learning it is more praiseworthy to do a mitzvah
that you’ve taken on versus doing it optionally, though it seems counterintuitive.