You are asking about the speed of the servo and I'm talking about the position of it. Two different things. The speed of the servo will be very difficult to detect. Knowing the position of it will be a lot easier and give you similar results. If you want to use the speed, then I'm unable to help you, as I don't know how to detect when a servo's speed varies. I don't know if that is even possible.
The way I see it is:
If the servo and pot are in the centre position, only the centre light will be on. Turn the pot fully to the right and all the right-hand LEDs come on and incrementally go out as the servo turns to the right. When the servo is fully to the right, only the rightmost LED will be on. Turning the pot fully to the left from this position will light all the LEDs and these will incrementally go out as the servo moves to the left, leaving only the leftmost LED on when the servo reaches the end of its travel. Any position that the servo stops between its limits will be shown (approximately, unless you have 180 LEDs 
) by which LED is lit.
So you will have a position indicator, which will also show you how far the servo (if it's moving) has to travel before it reaches the set position. How does that sound to you?
There's no point in doing any coding until you've got the parameters set correctly. You don't start driving until you know where you're heading for, even if you don't know the route you need to take. Otherwise you could end up driving 100 miles when you only want to go next door.