typical servo speeds

I'm enquiring for someone else, they wish to make a system to simulate
the flapping of a hummingbird wing or something of that nature, rather
than a fixed mechanism a fully controllable one is desired.

Assuming very low load can a servo motor oscillate at 20hz and if so
what sort of amplitude might be possible and what sort of
controllability? Also which servo types are preferred (pcb motors?)

Just looking for ball park opinions.

Cheers,

Graham