I hear ya and I do the same thing pay off my credit card every month and haven't paid interest on either card. Guess I should as for a raise haha. What do you mean pay yourself at variable interest rates?
It means that on months when there is a lot of money left, i repay more, on months when there is less left, I repay less. In the end, I repay a little more than I took, so my savings account ends up with a net profit. (it's kinda linked to what my wife looks good in and how much the latest drresses cost as well