he reason that I ask this is because the data that I send only ever has values between 0 - 16 from this line:
Sorry I missed that bit, that will prevent the data being confused with the the sart bits.
However note that in Processing the draw function is not quite like the loop function as it only gets called 25 times a second not as fast as possible like the loop function.
Try timing how long it takes your Arduino to read a frame. Sending data faster and it it working does not make sense unless it is taking too long to do the stuff on the Arduino side and the input buffer is overflowing.