I'm not sure about this. It seems to me that "intermediate speed" doesn't work particularly well for people at either extreme -- the fast people are frustrated because they can't go fast (unless they've resigned themselves ahead of time to having a social weekend ride, not a particularly working-hard ride) and the slow people are frustrated that they can't quite keep up.

Also, I feel like (with this weekend's group of people, for instance) the discrepancy is more in pace and less in distance, so a bail-out point doesn't necessarily help. (Well, it does, but not in the intended way exactly: if I try to maintain above a comfortable distance pace *for me* for a couple hours, I will happily jump on the commuter rail, partly because the activity isn't particularly fun and partly because I'd be feeling all guilty about slowing people down.)