What would it take to take down a mountain lion?
Poking it in the eyes and hitting it in the face has driven them off after an attack in the past. But that only works if they don't sever your spinal cord with a bite to the neck first.
Bear spray comes out in a pretty direct stream. It's not like a f'n bug fogger. It works well when it's not sprayed directly in your own face, which I would worry about with you.
The one you see is not the one you need to be concerned with at that time, but spraying it with pepper spray will make it think twice about getting too close to people in the future. Chances are, it sees you, too, and is not hunting ATM.
The one you don't see is the one that you need to think about. A rifle won't help you. A handgun, maybe, but you need to be able to grab it, unlock the safety, and fire it while you are in the cat's mouth.
I trust myself to hit the cat in the face more.
But then again, I wouldn't be out in a high risk area by myself. Small groups are MUCH safer, and ANY weapon used by your buddies will drive a mt lion off. Not necessary to kill it. It will give up when it feels threatened enough.