thank you for your hint, I'll try to determine that!
Are the essential USB/Serial chip specs the same as of the atmega328p?
update:
230.4k is supposed to work both for the Due and the AVR in the USB/Serial chip, right?
http://wormfood.net/avrbaudcalc.php?bitrate=115.2k%2C230.4k%2C250k%2C.5m%2C1m%2C2m&clock=16&databits=8