Yes we are both running futaba digital servos in our electric cars and savox digital in our gas cars.
Its wierd that when you turn down the steering speed on the 4PKS with any receiver other than a 614 the speed drops to very very slow straight away.
I hope this is just an set up issue on the transmitter as I really want to buy a 4PKS but dont want to buy heaps of recievers as i already have lots of 603's,
All recievers work fine with my old 4PK.