A borrower with a strong score but a thin down payment or debt ratios near the CMHC guideline ceiling may still land a middling rate, because the lender is weighing the whole file rather than one number in isolation.
Where score matters most is at the edges. Near CMHC's minimum insured threshold of 600, a small improvement can change whether a file qualifies at all, while well above that threshold the marginal effect on rate tends to shrink.
A mortgage broker can show you what your actual score and ratios translate to in rate terms, which is more useful than a general rule. Get your hand-reviewed valuation from Joel Dyck.