I have, AND ALWAYS HAVE HAD...

[serial]
car_rate=115200

because otherwise I always got strange pauses and slowdowns during regular MP3 playback as the player toodles along and writes useless stuff like "seek failed" etc. to the serial port.

For some reason, the GPS works fine even if I do that. I think it's because something else throttles it down to 4800 when it needs to talk to the GPS. I never understood it, it was all FM to me.

Would be interesting to see if you get the same failure modes with that setting.