Pull as long as you are comfortable and ride just hard enough to keep things moving.
The Tuesday night ride got canceled due to rain here this week, so some of the "fast crowd" came to the "relaxed pace" Saturday ride.
It was a 37 mile route through an area I ride often so I got designated group "GPS". I lead and took turns pulling though the long rollers and climbs of the ride. The last 10 miles, were a 2 mile fast decent followed by 8 miles of rolling flats. The pace lined formed on the flats and I could barely hang on but could not rotate through. They kept accelerating as each rider came to the front, I let the rider sliding back in front of me, and hung on.
While talking at the end of the ride, I commented that I could not match their acceleration and hung on the back trying to keep up. All the guys said was, if you want to ride fast, ride with people who are faster, and that I pulled all day in unfamiliar territory, and that I should come on Tuesdays.
No ego, no attitude, just sharing the sport.