my advice - i'm very new to doing long distances, the london-oxford ride was my first, at 70 miles. that was ok, if a little hard on the arse, definitely helps if you're doing it with lots of people etc.

recently i cycled to portsmouth on my own, a route of 45 miles. the wind was coming off the coast at me the whole way, and that 40 miles felt like 80. plus, being on your own, it starts to get a bit bleak.
Norfolk could also be windy, it often is, being so flat.

I would think that after 50-60 miles, you will probably be a bit fucked off with it, and the idea of doing another 9--100 miles will be too daunting!