I had a stab at this with some friends at the end of August. Set off from Winchester at 6.30am with a view to getting to Eastbourne before the last train back. We were doing OK for time (even accounting for a puncture and a leisurely lunch at Amberley) until one of the party caught a flint in their front tyre and crashed heavily just short of Devil's Dyke. He bashed himself up pretty well, although nothing broken. By the time we'd sorted all that out we weren't going to have time to finish the rest of the ride (especially as it gets hillier the further east you go) so we bailed and got the train back from Portslade. It's a box that needs ticking
Did Petersfield-Eastbourne and back over four days in the early 90s, that was a good weekend.
The double people are clearly bonkers, I can't imagine having the willpower to reach the end just to immediately turn around and go back the other way..