So, I decided to scope out the Malvern Midsummer Marathon route in August 2012. I didn’t follow the exact route due to a missing footbridge (swept away by the summer rains!) and an injury near the end making the descents difficult making in prudent to follow a flatter route for the last few miles. This was a good exercise in figuring out the target walking time and also the kind of terrain that can be expected. As well as the hills, the other main issue is the roughness of some of the footpaths making it very hazardous on the ankles.
You can view the data recorded and the route here.