That makes sense, as the 57 has a bump in the high mids that the 58 doesn't have quite as much of... i suppose I will allow it.They are, but that windscreen makes a difference. I hear the 58 as being a little warmer on the bottom. I actually prefer the 58 for micing bass cabs. And acoustic guitar.
Using a dynamic mic on an acoustic guitar is a crime against humanity though. Don't let me see you doing it, or I'll buy you a condenser mic! Don't test me!!
(All in good fun, my only rule for recording is sounds good = is good)