There is no score on the MCAT that one could achieve that would make GPA “not matter”.
You need a GPA of about 3.4 to be a credible candidate. In certain circumstances (difficult academic major at a rigorous institution) the bar might very occasionally go lower. The chances of getting accepted with a GPA of below 3 are extremely low.
Why? An admissions committee looking at a GPA of 2.4 and an MCAT of say, 43, thinks: very talented person, no work ethic. Medical school (the first two years in particular) is primarily dedicated to the rote memorization of a vast quantity of data. Medical school tests measure your knowledge of facts: either you know them or you don’t. The only measures of aptitude that matter are:
A. Ability and
B. Willingness
…to memorize said data. The MCAT is a reasonable measure of the first; GPA is the only reasonable indicator of the latter.