I've tried the 4PK and i really liked that it was jam packed full of features. I would have gone for the 4PKS but the price was an issue. But I got to test it and i like the few improvements they have made.
The new one has different software and a new button
Chances arw telemetry was added too but I'm not sure.
EDIT: Don't think it does surprisingly, ill double check tomorrow.
You'll find most racers dont use it, simply because we can't have one eye on the car and the other on the radio