Here's the VarSpeedServo library. It's a clone of the Servo Library with one additional function slowmove which is a replacement of write with an additional speed parameter.
Speed=0: Write is used, full speed
Speed=1: Slowest
Speed=255: Fastest. With the servos I have, above 127 I couldn't see any difference to write because the mechanical speed was the limiting factor.
Everything that works with Servo works with VarSpeedServo too. Important: Don't use Servo.h and VarSpeedServo.h at the same time, it will create conflicts.
Example:
#include <VarSpeedServo.h>
VarSpeedServo myServo;
...
myServo.attach (mainPin, ServoMin, ServoMax);
...
myServo.slowmove (newpos, speed);
...
Let me know how it works out.
Korman