You're going to see a lot of numbers thrown around, but those numbers are either complete ass-pulls or lacking in context. A 28-30 mph average for a Cat 5 crit is extremely hard to believe, although who knows, really? I'm a Cat 3, and the fastest crit I did all year was about 27 mph average. That was a HARD race, at a major event that everyone is peaking for. But I've done slower races that were harder still. Average speed is certainly correlated with the difficulty of a race, but not perfectly. Also important to realize that I cannot ride solo at 27 mph for 40 minutes, but maintaining that speed in a peloton is a different story. Likewise, the speed you can reach in a solo sprint on a flat road is only loosely correlated with sprinting success in a race, where tactics and positioning play a role, along with the fact that you are (ideally) coming out of the draft already going faster than the 26 mph you quoted, having made less effort to get to that speed in the first place.
[MENTION=3283]caloso[/MENTION] has the best advice for you thus far. If you are interested in racing, start attending the racing-oriented group rides and start building fitness and getting experience riding in a group. Forget about how fast you are going, for now. It's mostly a distraction.