terrymorse 

Garmin Connect says my average speed is 78th percentile, but max average power is only 50th percentile.

Speed is a useless measure, as it's dependent on terrain, wind, road surface, aerodynamics, etc.

But what is "max average power"? According to Garmin, it's the highest power recorded over a 20-minute or 60-minute segment. And it records as zero power any time you may have been stopped during that segment. I wouldn't trust that number for much of anything.

Training Peaks tell me that my 20-minute power (watts/kg) is 73rd percentile, my 60-minute power is 84th percentile, and my 90-minute power is 86th percentile. That seems about right (20-minute power probably is low because I'm not doing any 20-minute FTP efforts).

Training Peaks also says that my watts are about the 40th percentile. Which explains why the big guys can destroy me on a flat course.