If you hate Sallie Mae why don’t you have the loan assumed by the William D Ford Direct Loan Program http://www.direct.ed.gov. With 50 K in debt you have the opportunity of extending the term to up to 25 years.
I would personally elect to make an interest only payment. There is a little secret to the Federal Loan program that once you ache paid on the loan for 25 years the remaining balance is forgiven. I am not certain if the 10 years you have put in would be counted toward the 25 years http://studentaid.ed.gov/repay-loans/understand/plans “If you have not repaid your loan in full after making the equivalent of 25 years of qualifying monthly payments, any outstanding balance on your loan will be forgiven.”
Additional benefits of this debt. In the event event of death or permanent disability this debt is forgiven.
4% is not a very difficult hurdle rate to outperform.
