On day one I rode my own pace, stopped a bit more than usual and was never in an organized paceline. The temperatures ranged from the usual 12-14C at the coast in the morning to 28-30C in the afternoon (actually cool for the time of year). On bike time was 9:30 with a total ride time of 11:30. At the end of the day I felt fine and not really fatigued at all.
On day two, the whole club rode as a peloton for the first two hours, averaging 18mph. I then rode in a small paceline of four riders for the next three hours. The average speed dropped as the rollers picked up and some fatigue set in, but we still were averaging above 15mph after five hours. I eventually rode away from the group on the coastal rollers, some of which are 12%, and rode the final four hours alone. On bike time was 8:07 hours with a total ride time of 9:03. I did the century in 6:55 mostly thanks to the fast start. However, at the end I was really quite fatigued and at times on the bike it was a struggle, especially the last three hours as I had spent most of my remaining chips in the first hour of solo riding. It's possible that I would have gone faster overall if I had been in a paceline group for the whole ride, owing to the forcing effect of a paceline.
However, this morning it would be hard to get on the bike for another long ride and that is one of the the lessons of this story. Riding 10% faster takes more than 10% out of your body. So if you are riding a tour or a long brevet, you had better manage your pace for the long haul. On the other hand pacelines can definitely get you there faster but you have to be careful about being pulled into going beyond you comfort zone, which is all too easy.