Should I make extra payments on my IRS debt first or pay off my debts from smallest to largest?

We owe $26,000 to the IRS.  We also have $23,000 in credit card debt, $5,000 in a personal loan from a bank and $6,000 in a 401K loan.  Should we make extra payments on the IRS debt first or just pay my debts from smallest to largest?  If we need to make extra payments to the IRS, how do we go about doing that when I already have a payment plan with them?