Ok Gordon, let's play make-belief!
Let's assume we're in an alternative universe where HollyHobby has already saved the 20% deposit and we'll keep everything else constant.
Assuming a lower tracker rate would obviously increase the tax payable on the projected rental profit so this actually favours the tracker mover option.
Let's also ignore the fact that I think your projected rental profit is overly optimistic.
So, by cashing out the home equity and porting the tracker, the "saved" interest is now reduced to €6,100 (€140k@3.1%, plus €160k@1.1%) and your projected rental profit is still €7,000.
A positive difference of €900.
Is it really worth bearing all the risks (interest rate increases, tenant default, regulatory changes, etc.) for such a slim projected margin?
Is it worth the hassle?
Is it worth the negative cash flow?
Is it worth the opportunity cost?
Is it really an "extraordinarily good investment"?