After spending far too much time trying to figure out the Gstreamer Lame plugin (to use with Sound Juicer) on Gnome, I found out it is all badly broken and in the gutters. I just gave up and moved to the excellent Grip. Grip (like good software should) allows for a little bit of command line configuration of LAME and the following is a handy reference for VBR switches.

Command-line Switch Bitrate target (Kbit/s) Bitrate range (Kbit/s)
-V 0 245 220 – 260
-V 1 225 190 – 250
-V 2 190 170 – 210
-V 3 175 150 – 195
-V 4 165 140 – 185
-V 5 130 120 – 150
-V 6 115 100 – 130
-V 7 100 80 – 120
-V 8 85 70 – 105
-V 9 65 45 – 85
-b 320 320 320 CBR