57's are very uni-directional which may be good for off-axis rejection (which is one reason why they are ideal for snares congas and bodhrans, etc.) although their pickup pattern is a tad wimpy, I found, for the flute. It also depends if you are playing in noisy pubs or concert halls. I've used a Peavey 580 vocal mic with good results on both flute and vocals in a pub environment and I found it to be stronger and more dynamic sounding than the 57.

There are some pretty good clip-on condensers being made these days that also serve both purposes. I read an article on Jethro Tull in the March issue of On Stage magazine where Ian Anderson discusses his mic choices. He sometimes uses an SM58 with 8db rolled off (through a high-pass filter) at around 100Hz to get rid of the low wind noise and rumble.

The clip-on mic he uses is made by Countryman, a company in California, a condenser mic driven by the output of a radio belt pack which transmits to a receiver on stage in a rack with a mixer. It clips on the end of the flute near the lip plate and he uses a little pop shield over it. While this is oobviously a fancy setup, there are a multitude of choices in this dept. The best thing to do, Im sure, is to go and check 'em out at your favorite music megastore.