Originally Posted by SethAZ

Ok, well I consider the mystery solved. I turned auto-pause off on both Garmins, and have "every second" recording turned on both as well, and after today's ride they were 1W apart on their average power reading. It has to have been the difference in time recorded because of differences in how the two units responded with auto-pause turned on and the fact that on my rides I typically have to stop several times at intersections, however briefly.
[MENTION=116887]seattle[/MENTION]_forrest, the Edge 500 asks me if I want to calibrate each time I turn it on, and I do it, but the Fenix 5 only asked me to calibrate the first time I paired it. The number I'm seeing on the Edge 500 when I calibrate it hasn't really changed each time I did it, so I doubt that was a factor.

This also gives me a real lesson in why avg. power recorded isn't all that useful, given it can change so much just based on differences between recorded time and actual time and moving time and so forth. Now I need to familiarize myself with the other power-based stats like TSS and whatnot. Since I measured FTP yesterday and recorded it in my apps, I believe that TSS will reflect what percentage my ride's power output was compared to my FTP. That should give me a "zone"-like result similar to how I've always used HR zones in the past.

I did pull the trigger on a Garmin 530 today. I got a good deal at 15% off the normal price, so it was just over $250. I look forward to having the same connectivity and features that I've enjoyed having on my Fenix 5, while also having a slightly larger and easier to read and configure screen compared to my Edge 500.