I do not have a link for speed as requested, though in a tube rectifier I am not sure what the speed effect would be on sound. Not saying there isn't one of course.
This link has a pretty lengthy discussion on what effects tube rectification can have on the sound of an amp:
http://www.tubemaze.info/sound-of-rectifier/#comment-214Read down a bit as the first poster does not say much.
The only opinion I would have on what is written would be concerning the voltage drop. My feeling is that the reason rolling rectifiers has a noticeable effect on the sound is due to the fact the differing types run the follow on tubes in the chain at quite different bias levels. And that's just an opinion.
Hope the link helps some.