Will, thanks for taking time to post all the info! A wealth of info for builders.
One clarification, I wasn't talking about soft (vibration damping) mounts taking away power. I use soft mounts whenever possible - they reduce vibration and make long lasting airframes/components. The planes are quieter and smoother to boot and I've not noticed any power loss as long as its a quality mount.
I was referring to low quality nylon beams (whether on a hard mount or soft mount) that are not strong enough and can shake and flex under power. Those can lead to MORE vibration under power and some power loss.
The original Hyde mounts were awesome. I noticed the "adjustable" Hyde mount used adjustable nylon beams which did not look as sturdy as their aluminum beams, and hence the question how they perform.
I'll update on the Atlanta as I go along...