Is it worth revisiting whether it should be mentioned that the -V setting accepts fractional values?
Usage: -V<number> where <number> is 0-9, 0 being highest quality, 9 being the lowest.
Maximum quality is achieved when, regardless of listening conditions, you are unable to detect a difference between the MP3 and the original. As demonstrated by blind ABX tests, LAME-encoded MP3s typically achieve this level of transparency when encoded with the default settings, at bitrates well below maximum. Encoding with other settings will have no effect on the quality.
Maximum quality is achieved when, under optimal listening conditions (e.g. headphones in a quiet environment), you are unable to detect a difference between the MP3 and the original. As demonstrated by blind ABX tests, LAME-encoded MP3s typically achieve this level of transparency when encoded with the standard settings, producing typical bitrates well below maximum (for example -V2 to -V3, since LAME was historically tuned for transparency and to address problem samples at -V2). Once transparency is achieved, higher settings (lower -V values) will not produce meaningfully higher quality.The VBR scale has been carefully optimized, and permits the use of fractional values (-V9.999 being its lowest quality/bitrate setting), though some graphical user interfaces to LAME VBR restrict selection to the commonly-used integer values only. A change in the -V value (down or up) will respecitively raise or lower the average bitrate, and will also raise or lower the quality unless the threshold of transparency has been exceeded. As a very mature, well tuned, quality-oriented encoder, LAME already has the best 'commandline tweaks' and internal optimizations already built in to its VBR scale. Any further commandline switches are likely to degrade quality, to waste bits or to provide less bang for you bitrate than simply adjusting the -V value for the equivalent bitrate change. The lure of 'secret expert settings' can be strong, but the advantage of 'commandline tweaks' usually tends to vanish when subjected to ABX testing.
Regarding 320 vs VBR, IIRC there simply isn't an abundance of evididence showing one to be better than the other, rather depending on the sample and listener, either may show superiority when a difference can be demonstrated.
"-b 320 vs. -V 0" is more generally "CBR 320 vs. highest-quality VBR"
That said, we are still suggesting that -V 0 is potentially better than -V 1, and that's potentially better than -V 2, and so on.
I heard a DJ last week who should have used lossless. He was DJing for a kids dancing competition. His CD player failed to read one of the kid's CDs. No problem - he had the same track on his laptop. Problem was, the kid was using the version without vocals (for reasons that will become apparent), and he only had the vocal version. Ah, no problem again - the vocal cut feature in the software would sort that. If only it hadn't been an mp3. Vocal cut only works (sometimes) on the highest quality mp3s, and this one wasn't. The vocal bled through as horrible mp3 artefacts. It was so bad that he gave up and switched the vocal cut off. Just at the point where the lyrics said something like "...and you're no fucking use to me..." - as the five year old girl continued through her dancing routine. I doubt they'll be using that DJ again.
The higher the bitrate, the more you can do with MP3...
Thus, the recommendation would be to encode using the settings that provide transparency under optimal conditions (and you know everyone's going to go one higher out of paranoia). But we shouldn't say that transparency/"maximum quality" is only achieved under those conditions.
The fact that some of the settings are indistinguishable doesn't really matter to the user who wants maximum quality. They're going to pick the potentially best settings, and they're not interested in a lecture about how, technically, they could just as well choose lesser settings and be completely unable to tell the difference. *sigh*
isolated test samples by individuals