interest rate but remember the opportunity costs associated with a 401K loan or withdrawing the money for 60-90 days.

In most plans, when you borrow money from the 401K, you are cashing in investments in your account and re-investing the the funds in a loan to you. So if the market goes up, the portion of your 401 K that is tied up in a loan has lost opportunity. It doesn't go up with the market. It only goes up by the modest interest rate you are paying yourself.

The same is true if you withdraw money from the account and repay it in 60 or 90 days.

The purpose of your 401K is for the future, and you are betting on long term market gains. However, when you start pulling out money (withdrawal or loan) you might be losing out on market gains. Don't try to out guess the market.