Audax rides

I've actually signed up for The Dean (and a couple of others in increasing length further down the line) - I'm supposed to be staying in the Travelodge the night before so no worries there, however, I appear to be cutting it a bit fine with making to the last train at 23:15 on the Saturday following the ride, I'll need to be quite vigilant with time/avg speed to get it all done.

Are you doing The Dean? and is anyone else from on this forum?

I'm kind of doing it. As the organiser I'm doing it three weeks early to check the route. On the morning of the ride I'll be handing out cards and then heading back into the Travelodge for a bit more sleep before mooching around Oxford.

I wouldn't worry about the 23:15 train. On my first pass of this event I made it in that time and on the second I managed to catch the 22.10. Couple of key things for making decent time on this though;
1) The first 20k is pretty flat so get out the gate right at the front of the crowd and you'll get sucked along pretty quickly. Be sensible about when to unhitch yourself though.
2) Don't hang around more than you need to at the first control. It's outside and usually pretty nippy, you'll then make a longish descent and you don't want to be cold for the long climb to Ford.
3) After Winchcombe, almost all of the decents are fairly flowing so you can easily capitalise on them for speed.
4) You really want to be in Chepstow by 13.30ish and you want to be over the top of Hackpen Hill (after Royal Wootton Bassett with a big white horse on it) by sunset. If the conditions are dry and clear, you should be pretty safe to thrash this descent.
5) Try and get out of Membury Services with a group don't bother with the main building, just get into the petrol station like everyone else. The staff are used to it and it's funny to watch motorists deal with a motorway service station packed full of cyclists and stacks of bikes. Once you're over the top of the Ridgeway it's pretty much plain sailing back to Oxford.