Increase: +$0 per month
A "Stress Test" is a calculation used by lenders (especially in Canada under Guideline B-20) to ensure you can still afford your home if interest rates rise. Even if you get a rate of 4.5% today, the bank wants to know: could you still pay the mortgage if rates jumped to 6.5% or 7%?
Passing the bank's stress test is one thing; passing your own personal budget is another. If a 2% rate increase would force you to stop saving for retirement or saving for emergencies, you may be borrowing too much. It is safer to buy a home that you can afford comfortably, even in a "worst-case scenario" rate environment.