If I remember correctly, the average speed for the Cat. 4 races in Prospect were well over 26mph when I last did those races in the late 90s. I wouldn't worry much about being able to maintain that average as you're pretty much getting pulled along by the pack. The problem is a lot of guys sat in the pack and waited for the sprint at the end, so if you want to go it alone off the front, you would have to be able to push a bit faster than the average. My advice for the beginner racers is to get comfortable with bumping in the middle of the pack and learn to go in a straight line over those manhole covers and potholes that litters that road in the park. Oh, and don't overlap wheels!