Just how good is the 20/1.7?

I have the 20 and use it probably more than my other lenses.  The difference in focal lengths may be more significant than you think.  I used to do a lot of my film photography on a Minolta CLE with the 40mm Rokkor lens, so I'm very comfortable using a 20mm as a "normal" lens on M43.  You may not be, so check this out before you make this kind of change.