From my study about them. MT-4 is capable of FHSS-3, which is the faster receiver but you will lost the telemetry, FHSS4T. This means you can swap receiver to the faster one once your skill become better. I'm using 3PL right now but many people at my track are using MT-4. I'm waiting for them to switch to M12 so I can get MT-4 from one of them.