From what I can tell, there is some flexibility with how the SBC encoded content is streamed. You can manually set something in Android that forces a higher bitrate. Perhaps your phone is already doing this? I imagine that some stock ROMs might do that if they're optimized for your hardware (Bluetooth v3, v4, etc.)

I haven't messed with that at all since discovering the mpeg12sources thing. I will say that Pandora streaming from my Nexus 7 sounds better than Pandora streaming from my CM10 SGS3. Maybe I should look into this more....

It's hard to keep track of all this because, when on the Nexus 7, Pandora thinks it's connected via WiFi rather than cellular data. That fact alone could produce better audio from that source.