Just how good is the 20/1.7?

50mm having the FOV of a human is a myth.  Take a picture with a 50mm and then compare the picture with what you see...the human FOV is much wider.

Around 50mm was called standard because I think it gives the same perspective as the human eye sees - i.e. "the zoom seems about right".  Even then some would argue the real standard is actually 43mm, which would make the 20/1.7 closer to normal than the PanaLeica.