"VBR doesn't seem to have a max bitrate setting? Is it just that it will decide along the whole track?"
As you probably know, max bitrate for MP3 is 320. As you said, VBR encoding "will decide along the whole track." In other words, during difficult to encode parts of a track, higher bitrates (up to 320) will be used, and less difficult parts will be encoded using lower bitrates. This way, the encoder doesn't waste bits on sections that don't need high bitrates, and it doesn't short-change the sections that will benefit from the higher bitrates.
There are a several of ways to limit the bitrate, but still use VBR. First, just try encoding a few files using the different settings in the Quality drop-down list and see which of them gives you acceptable quality versus file sizes. Or, choose Custom in the Quality drop-down and then click the Advanced button. Then there are a few different options using what are called the
--alt-presets. If you want to shoot for a specific target bitrate, called ABR (average bitrate) then enter, for example,
--alt-preset 192. You can replace the 192 with any bitrate that you want. This will still encode using VBR, but will limit the upper bitrate to whatever value you have chosen. You can also use other VBR presets.
--alt-preset standard will give you bitrates ranging around 180 to 200.
--alt-preset extreme will range around 220 to 270.
Hope that helps a little. Mostly, you just have to take a little time and do a few test encodings to see what settings work best for you.
Rob