There are two questions here. There’s a heart-vs-head decision about whether you feel happier knowing you’re debt-free, and there’s the calculation of which would make you better off financially.

Mathematically, you need to compare your mortgage interest rate to your expected return from investing. If you expect a 10% return from investing, this may beat the gain you’ll make by getting rid of 3% mortgage debt. Another factor is that the win from mortgage overpayment is guaranteed, compared to a theoretical gain from investing. If your mortgage rate is above 5% I’d be tempted to overpay. Below that, it’s more attractive to invest.