Err - isn't that an average grade? I really doubt that if it has an average grade of 4.7% that you don't have 6% on it. Locally here we have Mt. Hamilton. At the top is an observatory that was installed in the 1900's. So all the components had to be trucked to the top in mule trains. Mules will not climb more than 6 or 7% but if you do the paved roads now you can find short 10% sections.