I have a single hole faucet in my Corian sink. It is pretty beat up after
only 6 years and I am replacing it with a 3 hole faucet. I have to cut 2
new holes.

The installation instructions call for 1 3/8" - 1 1/2" holes, but the posts
only measure 7/8". Wouldn't I be better off using a smaller hole? 7/8"
might be pressing my luck, but I have 1", 1 1/8", and 1 1/4" hole saws (but
no 1 3/8"?!)

I presume the extra size is to allow for incorrect placement, but I ought to
be able to get them within an eight of an inch. Or is there another reason
I am missing?

I don't have a whole lot of experience with hole saws, but I would imagine
that I can start to cut 1" holes and then confirm that the faucet fits
before cutting through. If it does not fit, then is shouldn't be too late
to go to a larger size, should it. (obviously once the hole is finished
there is no way to fix it...)

Thank.