I have read as a rule of thumb if you are truly between sizes to go with the smaller frame if possible. Reason being is that it is easier to change the stem to a longer one and retain good handling than the opposite, and a bike that is a little too large for you will be a bit harder to handle and heavier than the smaller frame size.

From what you say about your height, it sure sounds like the Felt Medium would fit you better than the Tall.

Good luck in your decision!