I personaly feel that DF bikes and Recumbents do not mix well in group rides especially on hilly courses.
I Ride the DF with DF people and 'bent with bent people. I see no problem with this kind of attitude.
Some here on this formum like Mr Evans promote the speed of recumbents over any DF bicycle. I mostly agree with him but not in all situations are recumbents superior. And lowracers especially in an urban environment are potentially deadly. I see threads on this forum on that subject. A bicycle is a tool and one must weigh all options when choosing a tool. Commuting or performance riding require different needs and the good ole DF bike is very handy in an urban environment.
Being faster and mixing well on a group ride are two entirely different arguments....
I think that it goes without saying that recumbents and DFs have different speed profiles, and that the hillier the route, the more pronounced the difference is. So, if matching speeds with your DF-riding friends is a priority, it would be better to use a similar machine. For me, the comfort of my recumbents is still a higher priority, so I am willing to accomodate the differences. Sometimes that means riding alone, other times it means playing leapfrog all day, and sometimes it merely means working harder on the climbs and riding the brakes a lot everywhere else.