OpenGL performance of persistent mapped buffers with READ_BIT

Hi!

Would there be a performance difference for a persistent mapped buffer between the two following mapping bit flags:

-  GL_MAP_WRITE_BIT | GL_MAP_UNSYNCHRONIZED_BIT

-  GL_MAP_WRITE_BIT GL_MAP_READ_BIT | GL_MAP_UNSYNCHRONIZED_BIT

If there is a performance difference - in what scenarios it could be seen?

Regards,
Aleksei