Any thoughts from the senior members of the forums?
Having reviewed > 7,000 MD-PhD applications over the years, I guess I qualify as a senior member.
Because there is so much variability among the rigor of colleges and the rigor of the curricula taken by individual students, it is not surprising that the SD in GPA is greater. An individual with a 3.7 from U Chicago is probably a stronger student than an individual with a 3.9 from Ball State. She may also be stronger than a fellow U Chicago student who earned a 3.9 because she took a more rigorous course load than he did.
As a general rule, there are three GPA thresholds: <3.3 = GPA is a significant concern, interview unlikely; 3.3 to 3.6 = GPA is a moderate concern, but can be mitigated by a strong MCAT; GPA >3.6 = no worries. There are other factors which can mitigate a middling GPA, such as the necessity of holding a job, rigor of curriculum, personal crisis, strong upward trajectory to the GPA, etc.
For the MCAT, you should think about this in terms of these thresholds: <28 = very great risk that individual will struggle in MD curriculum, interviews granted very rarely; 28 to 30 = risk that individual will struggle, likelihood of acceptance is around 15%; 31-34 = low risk of academic difficulties, likelihood of acceptance is around 33%; 35 & up = low risk of academic difficulties, likelihood of acceptance is around 45%. These percentages are based on the entire applicant pool; at the most competitive schools that receive a large number of applications, the acceptance percentages decrease.
To the OP, you should consider retaking the MCAT. You can get in with a 28, but you double the likelihood of acceptance by pushing your score into the 31-34 range.