I doubt that our 6500s will give you the missing 14MPH. In the end voltage will be the same as you will be at 6S but I expect the voltage to drop less under load due to the lower IR of the 6500s.

Another thing to note is the C rates claimed by factories and agents in China who sell Lipos are pretty much all made up. Since no one wants to specify how they get the C rate data there really isn't much we can do about it. This is why we use IR and make sure when we claim a C rate based on the Factories Spec that the IR will be lower if the claimed C rate is better.