We've got a group here in Austin like that. I ride with them usually once a week. They're nice guys but I almost hate riding with them. Why? The pace is so blasted fast, its almost not fun. But I realize it makes me a better cyclist and I'm enjoying the challenge right now. I got dropped, btw, last week because I unclipped at a light and the others caught it without unclipping (or did track stands). In the time it took me to clip in they opened a gap I couldn't close, and of course you can't maintain that speed solo very long. There's no shame in getting dropped. It happens - no biggie.
Oh and it is very possible to maintain mid 20mph averages in a group like this. I shake my head in disbelief after I do it with them. Working in a group though you can maintain that.
BTW, Lance Armstrong apparently showed up for this ride a few months before the tour w/Ekimov (some of the guys said he did anyway). Darn it - I missed that night. Figures.