Just a thought, there's a 4 day Bank Holiday weekend in early June - the late May BH and the Queens summat or other.
Scheduling the ride either side of a BH or weekend would mean travelling wouldn't have to be done in the week.
I don't know how long it'll take you guys to get from Brighton(ish) to Winchester - but if we travelled on a Sun and started on a Mon?
That Bank Holiday is likely to be the weekend that the Argus Appeal challenge takes place (although as yet its not confirmed dates for 2012). Doing it just after then could either be really good, or a poor choice, if the trail was badly chewed due to it being wet.
Travel from Brighton is a few hours by car or train, so not really a problem. I do think that if people can assemble the night before, we don't have problems contacting and waiting for possible attendee's if we go for an early start.