All interesting stuff - I've been advised by a chap at work that a club is the next step, but am a bit worried about keeping up with them, or not being part of a cliqué. Now that all these comments are here, I'll think I'll look into Audax and Cycling Clubs anyway.
I'm averaging just over 18mph (all things considered) at the minute, so going too fast in an Audax event isn't a concern, it was more the min/max speed and having that in your mind whilst on the course.
It's the distance/endurance cycling I'm really interested in.
The min/max thing isn't a big deal. It's better to work it out as times for the distance. So for a 200km ride if the min speed is 15km/hr. That gives you just over 13 hours to get around. If the max speed is 30km/hr then you won't be able to do it quicker than just over 6 1/2 hours. Just remember that that's the total time to get around the course. The clock doesn't stop while you're off the bike at a control.