Paying off House vs Investing in index fund

I have around USD 200 K in a 5 % interest rate account and have a loan of around 400 K on my house at a 2.6 % interest rate. I am already paying $1000 per month extra towards my principle but contemplating putting in around 100 K more over the next year. Really confused on whether to pay off the mortgage given it’s a really low interest rate or use that 100 K towards index fund. I already do maximize my 401K and have an employer match of 6 percent that accounts to around 2K per month on retirement. Additionally my wife also invests around 2K per month on stocks. I would save around 80K in interest if I put the 100K towards principle