"I believe being a federal student loan is one of the requirements. To my knowledge most other forms of student loans are not forgivable. Furthermore, you will most likely have to enroll in a plan that is based upon your income. Your 'minimum' payment may increase with a job raise."
*** It's a federal loan and it is forgivable. On the flip side, if my 'stable' career goes south in the next 5-10 years due to Medicare reimbursement changes I could go from making 93K per year to 70K (for example). Then, those $700 per month payments would be @ $450 and I would be kicking myself for the early repayment.
I wonder if it's worth not paying the debt off, and having $151,000 cash (minus the $30k for emergencies) compounding. It sure is nice knowing if anything happens those funds are available and not spent 'prematurely' to reduce a debt.
Anything can happen in the next 22 years and you never know what opportunities arise, right?
I'm not going to tell you to pay off the debt because it's a deeply personal decision that you need to decide for yourself after consideration of factors--many of them unique to you and unknowable by us. I, personally, would probably pay off the debt. But here are some of the factors I would urge you to consider, some of which have already been mentioned by others.
1. Is your income likely to remain in the qualifying range for the next 22 years? You mention that your income could drop to $70k next year from $93k. You say you would by "kicking yourself" because your payments would be $450. But realize that federal loan forgiveness doesn't mean that the federal government forgives your loans on a yearly basis. Rather, they just add whatever you don't pay to the total due, and at the end of 22 years, they write off the balance. So if your payments drop to $450, your total balance due will just go up. You say you have 22 years left, which I take to mean you're only 3 years out of school. Most people 3 years out of school aren't at their max lifetime earning potential. If your income goes up--due to the effects of promotions, raises, or even just plain old inflation/COL--and exceeds the qualifying range, you may end up paying back all of that money you are "saving" now, but with interest added. That's how the program is designed. Assuming your opening balance was roughly the same as it is now, you may end up paying as much as $1900 a month for as long as it takes (capped at 22 years) to pay off the balance in full, including that portion you think of yourself as "saving" now.
2. Are you likely to get married in the next 22 years to someone who also has an income? If so, you may fall out of the qualifying range and see above re: payment consequences.
3. Unless the laws change, you will have to pay taxes on the amount of debt forgiven at the end of 22 years, currently projected to be about $200k, assuming your income stays the same for the next 22 years.
4. "Anything can happen in the next 22 years" can go both ways. One of the things that can happen is that assets will begin to factor into required payments instead of income alone. This move would not be without precedent. Federal financial aid programs consider both assets and income, and many schools that ran their own versions of IBR long before the current IBR came into existence considered assets in addition to income. IBR is a very new program, and the kinks are not yet worked out. I agree with you that it is very likely to change in the next 22 years. I just don't know why you'd assume those changes are likely to benefit you, rather than the reverse, particularly since by your own admission you could afford to pay your loans if you wanted to. It seems unlikely to me that re-examination of the program will result in changes favorable to those who actually have the ability to pay.
All this to say that at the end of the day, I'd likely repay the loan. You're not a school teacher making $35k with $200k in student loan debt and on the 10-year non-taxable forgiveness plan. In that situation, I'd likely not repay the loan, even if I had the cash on hand to do it. You're really at the very upper end of IBR eligibility. I don't personally think of IBR as a "good deal" for those most likely to income-out of the program.