You noted that lame produces smaller vbr files than AC.

In the documentation of the command-line version of LAME (well the last one I downloaded), they said this:

Note: VBR is currently under heavy development. Right now it can often result in too much compression. I would recommend using VBR with a minimum bitrate of 112kbs. This will let LAME increase the bitrate for difficult-to-encode frames, but prevent LAME from being too aggressive for simple frames.

So maybe the reason that LAME is producing smaller files for some people is that they don't set a bitrate floor and it's compressing the simpler frames too much. When I use LAME, I follow the advice of this text blurb and set a minimum bitrate of 112. This actually causes it to produce slightly larger files, and I'm no longer getting the most "bang-for-the-buck" out of the VBR file format. Still, I am impressed with the quality of the LAME encoder although I haven't done enough testing to truly decide if it's better than Xing for the high-quality files.

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Tony Fabris