"the small diaphragm condensers like the C1000 ... have a slight splatter on the edge of sibilants"

To the sensitive ears of the pro audio world they are regarded as excruciatingly shrieky, while the SM57 is a respectable mic (if not always the absolute best) for almost any purpose.
It has nothing to do with diaphragm size - if anything small diaphragm condensers are likely to have a smoother off-axis response than large, and on-axis there is no generic difference caused by diaphragm size.

All the C1000 ever had going for it was that it used to be the only affordable condenser mic, (and you could use it battery powered if your PA didn't have phantom power) but the Behringer beats it hands down on price and, and while it's obviously not going to have the smoothness or consistency of a mic at 5 times the price it's got no obvious vices and a far flatter response than the SM58 you'll often find thrown up in front of any instrument on an average PA rig.

Better still, you can lose or break one on stage and not make a net loss on the entire gig...

Anahata