You make more money paying off debt earlier, instead of investing that same money at a possible return of 6% per year, I've done the calculations myself for my situation. You should do the same.
If I have $100 in an investment at 6% yearly and $100 in debt at 4% yearly, after 1 year I have $106 in the investment and $104 in debt, so $2 more than I had a year ago. If I pay off the debt now, I have exactly the same amount of money I had a year ago.
If I have $100 in an investment at 6% yearly and $100 in debt at 4% yearly, after 1 year I have $106 in the investment and $104 in debt, so $2 more than I had a year ago. If I pay off the debt now, I have exactly the same amount of money I had a year ago.