Bottom line: group rides make you stronger if they don't kill you.
Today I joined a group ride, most of the members being B+ level roadies. Everytime I join a group ride I have trouble hanging. Last time I went I got dropped after about 5 miles and had to suck the wheel of a straggler to finish the route.
This time I sought out the Venerable Fred, a 60+er classic white cotton sock Cambelbak wearing beater-bike riding Fred who can fly like the wind. I tell him my plan is to "stick with you until I puke, then aim the other direction". He seemed to understand.
I hung tough until we hit a series of hills. When I ride at LSD speeds I have no trouble going up these things, but at speed I felt like I was being fired out the back like a retrorocket. For ten miles I settled into a pattern: get dropped on the hills, then work like crazy to close the gap, taking advantage of my affinity for the Earth (meaning I'm overweight) and that I have a great bike that rolls well.
This time I hung for 16 miles until I pulled over to check my cue sheet. My heart rate had been pegged out at 160 so I just didn't have enough to try to close any gaps at that point. I rode the rest of the route forlorn and forgotten.
Depressed over my adverse power to weight ratio, I scarfed down a Starbuck apple fritter and some coffee. Life seemed to make more sense at that point.
And that is how I spent my day.