If you are living off your investments; i.e.: will be using your investments to pay the monthly payment on the loan, then it is all about the interest rate vs. the rate of return on your investments.
What this means is, it doesn't make sense financially to pay 7% interest on a loan while your investments are only returning 4%. In that case you would be further ahead to pay cash from your investments. But if you can get a fixed rate loan for 4%, while your investments over the same period of time earn 7%, then that's a winner.
So the long and short of it is, you need to make a reasonable projection of how much % your investments will earn over the same period of time as the loan and find a loan rate % that is less. Otherwise just pay cash from your investments. You really need a fixed rate loan because you don't want to be caught in a spiral where variable rates go up while returns on investment income goes down - that will kill your investments in very short order.
And remember, financial advice \ investment advice you get on the internet or for free is worth exactly what you paid for it.