@Maximum
Assuming an ECB rate of 2%, you will be borrowing money at 3% to invest.
This is not a good idea. You will be getting an uncertain return which, if positive, will be subject to tax.
Alternatively, you can invest at a guaranteed, tax-free and risk-free rate of 3%.
So you should pay your savings against your mortgage.
As an existing customer of ptsb your subject to their predatory lending rates for existing customers.
As an existing customer, the longest you can fix for is 5 years at 3%. Edit: Correction, you can fix for 7 years at 3%
By comparison, if you were an new customer you could fix for 5 years at 2.55% and get 2% cash back as well.
You should look at switching to AIB for 5 years at 2.35% which would save you €6,500 a year.
If rates go up before you have drawn down the money, then just stick with the tracker.
If you don't want to switch, then you could consider fixing for 5 years at 3%. If ECB rates rise above 2.1%, you would win by fixing.
But for the last three years you will lose out as you will have lost your tracker. But the balance will be down to €400k after 5 years and €300k the following year, so while you will be paying a higher rate, it will be on a lower balance.
Brendan