Bill, that's the nice thing about an enduro, you take the pace you want to go. Adrenalin certainly kicks in at the beginning but once you settle down you just ride and have fun. It's great to see that the Rocky Mtn. Enduro Circuit is still in existence as I was riding in their competitions back in the late 70's and early 80's. They had events from Chadron, Nebraska down to Los Alamos, NM with a killer ride in Steamboat Springs at the end of the season that was 125 miles of brutal trail. I passed Dick Burleson of Husky fame on a tight corner there once - the highlight of my riding career. He left me in the dust a few seconds later and I'm sure he was always had to deal with guys gunning for him when he was near so they could say the same thing I just did. It was a thrill anyway.
Just remember it's an enduro not a motocross race so go for it!