I'm just being unclear :-)
I've got an option to stay at a friends in Stratford about half a mile from the edge of the park (it's almost literally at the end of his road) on the Saturday night. Or I could drive to work in Greenwich Sunday morning (staff can park on site for free during evenings and the weekend) and then ride in from there.
Pro's for Stratford are more time in bed, less chance of a mechanical before the off, easiest of rides to the start
the Con is I'll be heading home from the wrong side of the river, although everything should be back to normal by then I hope.
Pro's for Greenwich are secure parking for the car, easier journey home once I get to it, possible chance to ride a route that's normally closed to get to the event
Con's are pretty much all the opposite of all the Pro's for Stratford.
I thought I'd read that the Blackwall Tunnel was open to cycle through in order to get to the start of the event further up this thread. If that's the case then it makes Greenwich the lead option, just 'because'. If I'm just all kinds of wrong and it isn't the case then Stratford pretty much wins all bets.
I'm doing the Freecycle on the Saturday with my wife but that doesn't really change my options, our life would be a little bit easier if I wasn't going on to Stratford, although equally she might just join me there rather than go home.