General Question about fast Serial Communication and Arduino
You are sending data at ~70kbps. Provided you use serial rate greater than this (115.2 kbps or faster on the Arduino) there should be no problem, assuming you samples are processed quickly enough. This seems to be the case.

Your problem seems to be on the Mac. With a quad core CPU on a fast multitasking machine this should not be an issue. If you are having problems this would be in how you are processing the data. I am not familiar with Processing but you could do this in any language. You need to separate the data logging from the processing and display task. This could be as simple as running a logger and piping the data into a display program.

This is not an Arduino issue (or even a Mac issue), you should ask on https://stackoverflow.com/. NOTE if you want help there you will need to give more detail of the code you are running in the Mac.