I accept the subjective comments about the "fast" sound of ribbon tweeters, but what parameter demonstrates this?
A decent soft dome can reach >>20KHz and it has to move sufficiently fast to be able to do that. Do things really sound fast if they can go faster/higher than this?
Some damning comments on ribbons here:
http://www.zaphaudio.com/nondomes/
Does the "fast" sound come from distortion?
OTOH these have amazing specs (at a significant price point):
http://www.raalribbon.com/download/raal_140-15d.pdf