I'm in a 7 piece working horn band.  I'm the drummer and I sing lead and backing vocals.  I have always used a Shure SM58.  A sound man let me use a Beta 57 one night.  I thought it was much too "bright" sounding.  He basically told me that the only difference between a Beta 57 and a Beta 58 is the wind screen.  The 58 windscreen sets the element back farther, which takes away some of the harsh overtones.  I switched to a 58 windscreen and it is a perfect vocal solution.  Clear, bright but without any harshness.  I have a 58  where we rehearse (the Beta only comes out at gigs) and I can hear the difference.  Save some money, buy the Beta57 and a generic 58 wind screen... you won't be sorry!