I just recently got a bike computer that does cadence. It's not a Garmin, just a cheapy normal thing. Anyway, I've always been curious what I spin, but I just try to stay in the gear that 'feels' right.

It turns out that I tend to fall in the 95-100 RPM range on a flat. What I did notice was that I have a fairly small cadence range where I feel comfortable. Once I get higher than 105 I feel too 'spinny' and below 85 I feel too 'mashy'.

My guess is that I'd do myself a favor by intentionally riding out of my comfort range to be able to feel efficient from about 75 to 110 RPM. Just a guess.