Toller wrote:

I have a 2 1/2" diameter fingernail bit. I only wanted to use the
top part
of it, which is only about 1" diameter. I figured that full speed
would be
okay, and it seemed to work out; but I wonder if the speed is for the
bit,
or the part of the bit I actually used?

There is no free lunch.

The centripetal forces are applied to the entire bit, with the max force
at the largest radii, not just the part that is cutting.

Consider yourself lucky that the bit was probably conservatively rated.

I would not suggest going there again.

Lew