Pay off the Mortage and be done with it.
You may be able to invest and get better than 5%, but how much better? In order to be worth it, I would say you would need to make at least 7% return on investment, which is possible, but certainly not garenteed.
COnsider how much tax break you get for the mortgage payment interest also, you could add that onto the % yeild from investment.
Also, consider that with the mortgage paid, you cold take that $1050 each month and invest it in whatever you want, vs. if you take the lump sum and invest, it might be hard to make portfolio changes, like if you put it in an IRA or group investment (i.e. 401K plans)
The choice is yours, but I go with the certain thing. Pay off the mortage and never worry about loosing the place you live due to job loss or whatever. Invest as you go.