Thanks, as always, Hermes, for the great information.

I definitely think the stiffness enhanced power transfer. It's hard to believe that the small amount of flex in the other bike made a huge change to the ride efficiency, but the difference felt quite tangible.

In addition to the effects you quantified, there are definite geometry differences between the two bikes. The head tube on the Felt is shorter and the bars are lower. Also, the fitter at the LBS put my saddle up a little higher than where I have the Trek... And, I think the BB is a little lower on the Felt. I could probably reproduce some of this on the Trek - slam the bars (there's one spacer left on the head tube) and raise the seat a little, and that would diminish the differences.

I really didn't expect much difference in speed and I"m willing to believe that some of it was placebo effect. But some of it wasn't.