10- bit ADC = 2 byte
6 microsecond/sample or
166.000 sample per second
..................................................
baud-rate: 333 kBytes/second
I have used speeds beyond 115200 on an uno and 2009, see - http://arduino.cc/forum/index.php/topic,61498.0.html - The ide could not manage but external apps like putty.exe did very well.
Give it a try