I have seen that the IRS pays overpayment interest rates that seem to range from 3-8%. When I see these rates are they related to what I pay in taxes? I.e. if I vastly overpay my taxes does this mean I will see return rates of 3-8% interest on what I overpaid in?
The rates have nothing to do with your tax rate. The rate in those tables is the federal short-term rate, plus 3%.
As for using overpayment of taxes as a high-yield savings account, let us know how that goes. :)