Current bitrate equivalents for quality modes?

Hello,

While tweaking the stream configuration interface in the Airtime
broadcast automation tool (http://www.sourcefabric.org/en/airtime/) we
noticed that Liquidsoap uses the zero to one scale for Vorbis quality,
rather than the more familiar zero to ten scale used by oggenc. It seems
I'm not the only person confused by this:

http://ffmpeg.org/pipermail/ffmpeg-devel/2009-January/067964.html

Airtime tries to hide this complexity by offering a choice of equivalent
average bitrates, similar to the table here:

https://en.wikipedia.org/wiki/Vorbis#Technical_details

the idea being that Airtime users will get an idea of the bandwidth cost
per listener, and more easily be able to compare Vorbis against MP3 or
other codecs.

However the Wikipedia page hints that libvorbis 1.2 usually compresses
better than the figures given. We typically use libvorbis 1.3.2 from
Debian wheezy or Ubuntu Precise LTS.

Does anyone have a table of equivalent bitrates for libvorbis 1.3.x? Or
is there a way we can measure the real bitrate of a Vorbis stream for
ourselves, e.g. from an Icecast stream?

Thanks!

Daniel