Actually quite an interesting question.
If you new all the theoretical tolerancing, ie say 10% allowance and set the cruise control against a really accurate sat nav speed reading of 55mph, so a true 55 which if the camera was set to 10% shouldnt see you caught theoreticaly.
Basically the question has to be how much effort is put into the setting up of the allowed time to cover a stretch of road.
1/ the supposed route
2/ the actual quickest route a-b that was possible
3/ the actual quickest route without breaking the rules of the road

Personaly i always set the cruise control thru specs cameras and know most of the common speeds real speeds off my sat nav and set the cruise control to them rather than my speedo reading, ie 60mph is 64 on my speedo and 70 is 75 (as near as damit lol), just doing that and not pushing for the 10% tolleraance normally sees you passing most things quite well lol
As a side note, everyday I drive to work along a 70mph camered road, and nearly every car is driving along at about 65 mph and as soon as they see the actual camera they brake ??? WTF its not like it just one and they might not be sure of the speed limit, there is like 5 along a stretch of a few miles, so its like 65 brake 55 accellerate back to 65 camera brake 55 accellerate back to 65 etc, pisses me right off !!!

Steve