MLC,
Not bonkers in the slightest.
I do a similar thing too, I cycle from Thorpe Bay to board the train at Chalkwell - nice route along the sea front - then alight at Limehouse, before a commute across to WC1. This has two great advantages - 1. Saves around 25 quid a week and 2. I get a good 15 miles a day cycling. Once the better weather comes I may get off the train even earlier in the evenings
ChrisKH,
I also use the Fenchurch St line, and would be interested in a "summer" commute back from the city to Southend.
Do you know how long it takes at a less "sporty" pace? I would be on a folder,a Dahon Speed Pro TT, but it should be good for that kind of ride/distance.
Iain