Downsampling speech files with lame

I have a large audio book that was ripped naively. It currently takes 1.6GB to store it, and I'd like to make it fit on a single 600MB compact disk. This invocation seems to be just what I need:

lame --preset voice oldfile.mp3 newfile.mp3

A test run on a small track from the book resulted in this:

[rday@snapper]$ ls -l 00p01.mp3 blah.mp3 
-rw-rw-r-- 1 rday rday 591872 Jul 17  2005 00p01.mp3
-rw-rw-r-- 1 rday rday 259344 Oct 26 10:03 blah.mp3

Hmm, is that a 43% reduction or is the new file 43% of the original... Anyway, the quality is very good and the compression is in the right ballpark.

The mp3 tags are all stripped, so I'll have to make sure I maintain the tag info in the directory and file name.