length of step/dir lines G340

I have seen several past posts regarding problems with the encoder
signals o Gecko 320/340's.
HAs anyone tried locating the amplifier close to the
servo to reduce the length of encoder wires?
Would this reduce the problems with "noise"?
Of course it could mean you need some capacitors located close to the
GEcko,and maybe some "help" for the step/dir signals.
How far from the supply can I locate Gecko 340?
2',4',6',? For my gantry it could be as much as 8' of cable carrying
70-75V up to 20amp,7amp continuos.

thanks
Carl