Ok, I'll going to put up a modification of the standard Servo Library which adds a method slowmove, where you can add speed parameter. Then you just have to replace your myservo.write (xxx) with myservo.slowmove (xxx, speed).
I wanted to polish that library a little before publishing, but it might just do what you need in its current state.
I'll post a link once it's up - I hope it will be today.
Korman