Its not pathfinder per se, but they do have CoC d20 rules out there that i would look at. I got the book some time ago and its a very interesting read and converts CoC to the d20 rules to easily grasp.
But as far as using just pathfinder, nah. To many classes with abilities to stop fear and are designed to be powerful while CoC ur trying to convey the PCs are just insects, mites, to the great unknown and pathfinder seems to make PCs that are big enough to slap and get a great unknowns attention at early levels.
I've used the D20 COC, it has it's issues but is workable if you are willing to convert old adventures into a new system. And I agree about the classes and the feel... it just doesn't have the sense of desperate imminent doom. Though I think with the proper uses of mad cultists and building a good sense of paranoia... it could maybe work. Not entirely wanting to go where none have gone before... but Dammit Jim I am a DM.
With the players I have, I think they will help sit the mood. They are looking for Role in this than Roll. One has already stated they are going to watch the Great Gatzby again to get into a mind set. Another has set up a rather sweet background idea.