Funny, that's almost exactly what I used when I encoded the Lord of the Rings series. That, however, was in stereo, using LAME ABR to get 64kbit average. I tested a bunch of different rates and 64kbit was the one I thought introduced the least artifacts (yes, there were some) without too much overhead.

Audiobooks on long trips good!

Paul
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Owner of Mark I empeg 00061, now better than ever - (Thanks, Rod!) - and Karma 3930000004550