You are a rare exception in being able to focus on your own training goals. When I was racing, I would usually lay down the early winter base by myself. Part of the reason is that you build up a lot of toughness just being out there by yourself in cold and miserable weather. The other reason is that if you go on group rides in the winter, there is always at least one clown in the group who is not a real bike racer but has something to prove, so the group ride becomes a hammerfest as everybody else's ego gets threatened.

It's usually understood that the pace is shared on a group ride. This allows everyone to get the benefit of being in front and being sheltered in back, and it also develops everyone's pace line skills, which are the fundamental core of bike racing, if that's what you're training for. The only place where this isn't so much the case is on randonneur rides, where one guy might hold the lead for hours and hours, and everyone behind him is perfectly content to let him do so. But if you're stuck behind in this situation, and you want to assume the lead, the best place to do this graciously is on the climb, where the deck tends to get shuffled anyway. Just zip past everyone up the hill until you're in the lead at the summit, then return to the original tempo.

Luis