No doubt, but at about 28 mph that sounds like fast paceline, group ride stuff or some really hard solo work. I got the impression we were talking about moderate riding. I don't see how the question of what ring to ride on the flats even has any relevance if you are talking about near-time trial efforts. I mean that's large ring stuff automatically, right?

Not too many folks claim average speeds for their riding of over 18 mph. Let's say the climbs hurt more than the descents help, so assume the flats make up the difference and run at about 20 mph. That would put you solidly on the 39/15 right in the middle of your one-tooth jumps on the rear 11-25, 11-speed cassette. I would much rather be riding there than on the 53/21 in the middle of the 2-tooth jumps. And interestingly, if I wanted to fall in with you when you were passing me on one of your power efforts, all I would have to do would be to shift the front.