I found the analysis section on this site http://www.r3mix.net/ to be quite informative.

The bottom line is:
"Radium FhG Codec in HQ & Stereo, Newer FhG encoder found in MM and Nero in "lowest quality" & Stereo and Lame vbr JS or Lame 256 cbr JS all produce sufficient quality for archiving.
LAME >= 3.80 -b256 -ms -h 256kbit/s (Joint) Stereo is distinctly the most accurate mp3 encoder (Best archiving for cbr)
LAME >= 3.83 -V1 -b128 -mj -h VBR is by far the best overall (highest quality/size ratio) archival mp3 encoder "

The site seems be quite pro LAME, but that may be well justified.

I think I'll have a more serious play with LAME.