With one exception, it's usually the opposite for me, because we get more leisurely and talk instead of focusing on the ride. I do have one friend that bumps my pace up (even while chatting), just because he's so much faster than me, even when he's not pushing the pace.

Oh, and to answer the original question, a couple of solo centuries would be my longest solo rides. But 80% of my riding is solo, so I'm doing 60-ish mile solo rides just about every weekend.