@cwordman 5 years is a rather short time frame when it comes to investing. So it's not reasonable to expect a 7% average over that time period, certainly not on a risk free rate.
But I also can't follow your math.
@nariko Why don't you just keep your variable rate but make your payments as if your rate was 4.84%.
It's the same effect on your monthly cash flow, but in the meantime you're paying off your mortgage faster because your current rate is lower.