Okay, again I don't have the same setup, but I was able to test my FTDI cable to Serial1 on my Mega2560 on a Mac Powerbook 10.6.8. The ASCIITable sketch did run okay to Serial Monitor (I tested both 9600 and 115200 baud ok). I do have a few more FTDI cables and boards I could test with to see if test may vary any.