I may be off track here a little and excuse me if so. The track condition in regard to firmness, the moisture, and the lenght of grass is one factor in the speed of the race. The atmospheric conditions such as air pressure and the speed and direction of wind is another factor. The racing style of the horses within the race is another. Then there is the jock. Very few races are won by the winning horse jumping in front and going fullbore to the finish line.
Invariably if the winner gets in front and stays in front it will only just fast enough to fend off any challenge. often the winner will be the horse that runs the leader down. Hence the speed a race is run is individual only to that race. Records happen when two or more horses are vying for the same position in the field.
Regards Beton