you should do an A/B comparison of the Beta87 and 58. personally, i think the 87 blows the 58 out of the water, but if you really want to decide for your own purposes, you should test the two yourself as well (just a suggestion from experience).
just another man's opinion-
I have a/b/c an d'd them and also cross referenced them betweeen some drums, bass,vocals and even a trumpet. While they are not the greatest mikes ever produced,I found them very responsive and clear in the
aforementioned applications. But my reccomendation would be to use them vocals as
they perform without much coloration and their 3-point pop-filter comes in handy when
miking the next Mariah Carey!
For the studio assuming this is your main vocal mic, I would get a Rode NT1 before I'd use the Beta 87. For live use on a stage, you need to have a good PA to use it. You need good feedback control because the mic is hotter than most stage mics. I would lean towards using a dynamic mic in most small venues. This mic demands lot's of space.