NB: new Meon Valley route adds 2.2 miles to distances
As I said on my 'home' page, I am mid-50's so I tend to ride at a steady pace, average 8 mph, or 10 if better surface etc, whereas a few years ago 10 to 12 mph. Also, I find that I am more cautious, (or is it clipless pedals?). On the BHF rides and on Trailbreaks website, times are generally similar, though several take a few hours off. I have read of a pro. rider doing Winchester to Eastbourne and back in 24 hours. Trailbreak do supported rides and even a night ride !
The following site has some very useful distance tables, eg along the way, roads for rendezvous, distances to taps http://www.southdownsdouble.net/routeinfo.html
Also, simple arithmetic, at 8mph, an extra 1 mph average reduces time by ONE hour!
Aug 2010: I have updated distances to include new Meon route via Exton March 2009: