In reply to bouldery bits:
It was basically trying to average 5mph, which I did apart from having a short break to buy a drink and get my water bottles filled up at the Top Brink. The first few hours I was making a conscious effort to slow down and keep the pace near the desired average, obviously it required a bit more effort later on.
I think I could probably have done it 2 hours quicker, but it was my first attempt that that sort of distance in the hills and so took a pretty conservative approach. It was a personal challenge rather than a race.