(sorry for the bump)
Speaking from a similar experience and numerous listening/analysis tests, newer versions of LAME simply aren't as good when it comes to CBR encoding. This is because developers consider VBR encoding to be a superior method (same quality, smaller filesize). If you need to use CBR encoding, I highly recommend YAMP 1.3.
That said, I agree that 128 will never result in very good quality (unless you're encoding a mono file, which requires less data).