Near a bad smell, one might want to do Sh'ma, the Amidah, blessings, study, or think Torah. Is halacha equally strict about all five acts?

"Just as one separates oneself from excreta, urine, a foul odor, a corpse and the sight of nakedness for Kri'at Shema, so too, he should separate himself for Shemoneh Esreh". —Rambam. Hilchos Tefillah 4:8 in translation.

The Rambam just discussed:

1) Sh'ma.
2) Sh'moneh Esrei.

He didn't discuss the acts of:

3) Saying blessings.
4) Studying Torah aloud.
5) Thinking about Torah matters.

When there's a bad smell nearby, is Jewish law equally strict about all five acts? Or is it stricter about some and more lenient about others?

Please cite sources.