I actually knew about Speex for as long as I was playing with this one encoder for 3 years now. Speex is Vorbis below 32 Kbps. At 32 Kbps Speex sounds more distorted with annoying clipping than Vorbis and saves 5 KB. Think of the old LAME 3.84 or Blade or Xing encoders in 2000 and Speex is exactly like that at low bitrates. I tried it in Firefox 3.5 and no support yet.
As far as my knowledge to achieve aotuv vorbis below 32 kbps, you must convert the podcast to 16-bit PCM first and then Vorbis can compress it down to 16 kbps with a front end GUI. That kind if erases the need for Speex at 16 kbps. This AlexSBrown does his speex at 8 kbps in narrowband, but I cannot get mine to sound nearly as good.
I am wondering if anyone would prefer future podcasts at 24 Kbps Speex instead of Vorbis? If I don't get an answer, I will take it as a no.