Just checking the forums and no one replied to you.
The Gibbet is a hilly one! Uphill first half, along and down hill the other half. If you can run 5 miles you should be fine. The hills are not mega hard just a bit of a drag. I love it though! Good sense of achievement when you reach the top and see the views from Gibbet Hill.
Good luck all you Midnight Marathoners! I'm out the same evening laying out the course for the Harting Trail Race nearby. Ignore all yellow signs and mile markers. I'll leave the sign directing runners off the SDW until the morning. I have also heard a few runners are doing the 5, marathon and our race!!!! Best of luck with that! Our brave start sweeper is doing the Midnight. Might have to prod him a few times to keep him awake!