Well done review. And yes, its the speed that makes the difference. Clean leading edges on transients and proper control of decay characteristics is how I hear it. Comes closer to a "live" sound on acoustic instruments than any other driver type I'm familiar with, although I suspect electrostatic phones could be a contender as well.

new Raals ribbons announced

Looking forward to this as well as the RAAL tube amp to drive'em with.
Spent a couple hours with my SR1a driven by EVO400 this morning, wonderful sound!