Sheer madness, yes.
R20 using 58t x 14t with 406 wheels, hilly terrain, 5:40am start, -2C.....I did it Sat 22nd.
Time: 6 1/4 hrs, not brilliant but considering the limitations of a SS, I'm happy. Really needed a lower gear for climbing and higher gear for descending and fast flats, maybe use one of my old 3 spd SA hubs next time?
R20s are fun