Just a quick update. I wrote a simple routine that sends out a ctl-E and if there is a response I continue with sending the serial data.
The serial data in my program takes 70ms to execute.
The routine that checks for a terminal response takes about 1ms to execute (serial port at 115,000)
So, it looks like I can save 69ms each program cycle by using a routine that checks for a terminal response. Below is a copy of the code in the event it is useful to someone else.
unsigned long start, finished; // Timer variables
start=millis(); // Start timer
Serial.write(5); // ^E enquiry character
//delay (50); // No delay was necessary, but initially had it in the code to test it out
if (Serial.available() > 0) // Check for serial data response
finished=millis(); // Stop timer
Serial.print(finished-start); // Print program execution time to terminal window
Serial.println(" ms ");