I found that I could get adequate voice-quality results at 8kbps - if I forced the sample to 22k, selected mono, --nspsytune and --athtype 3
16kbps was ample, but do NOT allow it to select a wooly 11k or 8k sample rate - force it out to 16k or 22k
(I used razorlame to set the parameters - there are a good many other lame frontends as well)
I'll have to check out those presets though
PS. there is also --alt-preset CBR <bitrate>
If you need CBR.
PPS. Probably of no significance here, but it's a good idea to stick to 11k, 22k and 44k sample rates, as the lower 2 will resample to CD a lot more easily tham 8k, 16k and 32k - and if you may want to go audio CD "on the fly", best to stick to CBR as many programs make a complete hash of VBR (and probably ABR too).