RE: Reason for not upgrading to 2.4
Faster response time is significant for Futaba 10C. I am sure every user of 10C can see it comparing to the 9C. I believe 10C's response time is the fastest, according to earlier this year's benchmark (done by a heli pilot).
To appreciate the faster response time, one really ought be able to see the drift of the airplane as early as possible, and make a movement on the stick(s). With 10C, he will see the response of the airplane (almost) in real-time.