BTW, Arduino supports far more baud rates when tweaked a little. See - http://arduino.cc/forum/index.php?topic=138497.0 -
I got the Arduino also working on 345600, 400.000 and 500.000 but only for small (<10 ) char bursts, mainly sending.
Teensy2.0 however has the fastest Serial IO I used so far (claims 12 Mbit IIRC)