The improvement that you showed in your GPA over time will definitely help. And the fact that you did well in your major will be of some benefit.
As you said, to show that you have the intellectual horsepower to make it, you definitely need to do well on the GMAT to make up for the undergrad GPA. You should definitley be shooting for a 700.
Your Masters will probably help a little bit, but not nearly as much as a strong GMAT.