My wife and I are doing the PSLF. Don't put a cent more than they ask for for the IRB---it's getting forgiven anyways, so you're throwing money away by overpaying. At the rate that you are underpaying your loan, no amount is going to protect you against the threat of the PSLF disappearing and being stuck with a ballooned balance.
It's also not an issue of the PSLF program disappearing as much as it is going to require higher and higher costs moving forward to stay on IRB. ie- the trick of filing married but separate is rumored to be going away soon. I've met with two separate financial advisers who both suggested the program, with the knowledge that we should expect our obligations to rise, not fall, as the program continues to get revised. But either way, you file, setup your account or whatever, and you're in. They're not going to just fold and forget about you.