There is another factor to be considered. The point at which the track is measured does not indicate the actual distance traveled. If the track is measured close to the bottom but the racing line is at the top of the track the distance traveled will exceed the distance that the track is using to convert speeds. Speeds therefore will appear to be slower than what it actually is. Conversely a track measured at the top, but with a low racing groove will result in cars traveling less than the actual distance of the track and can result in speeds quicker than they actually are.

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As an illustration of my point traveling .450 miles = 2376 ft, .5 miles = 2640 ft, .550 miles = 2904 ft. A difference of 264 feet for every .05 of a mile. Obviously factors such as grip, banking and turning radius make up for traveling that greater distance at some tracks.