Okay, I'm getting conflicting advice both here and elsewhere.

The most popular option would seem to be a low-quality mp3 (192kbps = 7MB per 5 minute track) and a high-quailty ogg (256kbps = 9MB per 5 minute track). I'm keen to 'get it right' as I won't be able to produce higher-quailty versions once access to the equipment capable of reading the original tapes is lost. I just don't have the facilities to archive copies on DAT tape or offer more than 3MB/minute to the material.

The copyright holder is wary of licensing costs involved with the mp3 format but is willing to allow mp3 distribution on the Internet if covered by a suitable indemnity contract.