I forgot to check my computer before I packed it up, but I'm guessing I probably averaged around 13mph myself on this tour.
In general, folks rode at their own pace and visited with one another at the rest stops. A few folks (mostly couples) stuck together in groups of 2 or 3, but the vast majority just took their own sweet time. Fast riders tended to finish up around 2 in the afternoon (after having left around 8 or 9) and the slower folks didn't get in until 5 or so. It was never a problem and I don't think too many folks were SAGged in, although a few folks chose to do so.