Well, my experience with PPTC is:

According to the description of their ride classifications, I am a CC rider. However, in practice, people who show up for the CC rides that I do are not necessarily in that category. Apparently many people choose rides based on start location, route and distance, regardless of their usual average speed. Add to that the fact that I'm slow going uphill, and I usually get dropped by most of the group early in the ride.

However this does not really bother me. So what if I'm slower than they are? It doesn't mean I'm any better or worse as a person. And I'm not so much slower that I never see anyone else on the ride. There tends to be someone just up ahead or not far behind me, and when I get to the rest stop there's still a crowd of people there.

I don't know about the C rides because I haven't tried any; they're generally shorter than I want or include a long lunch stop or otherwise do not meet my needs. I have heard from a friend that the C rides tend to be more friendly than the faster rides. And based on the ride descriptions for D rides, they seem to be much more social and laid back.

There are some combined C/D rides, so you might want to start with one of those to see if you like it. You can try one or two rides before you join to make sure you really want to spend the money on membership. So worst case scenario is that you conclude that it's just not the right group for you, but at least you tried.