I'm getting the distinct impression that VDSL1 & VDSL2 are completely different technologies with the misfortune of sharing an acronym and physical medium.  It's certainly far too easy to confuse data about one for the other.

Ideally, I'd like to see measurements on a real line to corroborate one way or the other.  However, the use of a fixed-size word frame does sound much more elegant than HDLC.

- Jonathan Morton