photonick - you should invest in a computer with avg cadence if you can. It's one thing to spot check your cadence, it's another to see what the avg is over a whole ride. The slow bits really bring down your avg cadence.
I thought I spin okay but my avg cadence on some hillier rides is usually in the mid 60s (I typically maintain 80s and 90s on the flats). Flatter routes, mid 80s if I work on it. On the trainer, mid 90s for an hour or two. I used to be able to maintain 120 rpm for an hour or two on rollers but that's no longer the case.
As far as avg speed, based on going medium (135-137 avg heart rate) I go about 18 mph on a flatter route for 2 hours. Hillier riders are harder, I might avg 145-150 and avg 17 over a similar time. When I wasn't training as much as I am now, I'd go about 15 mph on flatter rides and avg 145 bpm. For me a hard ride is avg 155-158 bpm but inevitably I don't go much faster than 18 or 19 mph for some reason. Races I might avg 165-168, which is normally about my blow up bpm.
Add 2-3 mph avg for riding with 2-3 other people. Add 8-10 mph avg for racing.
cdr