While on paper (and youtube) new servo is much faster, on track it doesn't magically make the car handle better. It helps with high speed manji sections and recovering from mistakes though.
Savox SC-1257TG:
http://www.savoxusa.com/Savox_SC1257TG_Digital_Servo_p/savsc1257tg.htm
Towardpro MG996R:
http://www.dealextreme.com/p/mg996r-metal-gear-digital-torque-servos-with-gears-and-parts-35763
