BG, if you're tooling along at 100 rpm on a 21/39, I'm in the 50/16 and spinning slower. A compact crank with an 11 or 12 small cog spins out in the mid 30's for me. If I'm going that fast it better be downhill!

I have compacts on some of my bikes, and standards on the others. Average speeds on all of them are just about the same. But if I'm heading out to Skyline Drive or Thunder Ridge, it's gonna be on a 50/34.

Yes, a compact does yield some lower gearing if that's what you're looking for. But for most casual everyday riding, even around here where we have real hills, a standard double with a wide range 12/28 set of cogs will get you up and over pretty much anything.