Very fast greens are 20 % faster than normal, i.e. 36 feet for a 30 ft putting stroke.
Due to the softer stroking, elevation has more effect than on slower greens.
Rule of thumb: 1 foot length for 1 inch elevation.
These two can be entered into a linear equation - use the rule of three.
Side slope also has more effect than before - be sure to aim further out and allow for the longer rolling track.
The green speed also affects the roll of pitches and chips as well as the other shots from outside!
In rated multiplayer games, you will notice that the green speed always follows the highest tier player.