Unless I actually planned to ride with another person, I figure on riding by myself. I usually end up linking up with someone just before or after the first rest stop that is riding at my pace. For 55 miles I wouldn't plan on pacelining anyway. Riding with groups I've found the majority of them start out too hard, then straggle in at the end. The two centuries I've ridden were almost totally by myself with no drafting, less than 10 miles total both times.
A more experienced rider in my club once told me for a long ride; "Start out slow, and taper off".