I used to race a Lotus Sunbeam and used rolling roads to fine tune the set up. The power figures are really only meaningfull when comparing before and after. Even then it should be back to back on the same day since atmospheric pressure can affect readings up or down (colder damper days will show more power due to the greater density of incoming charge). Also different rolling roads tend to give different readings so the same car with the same set up on the same day can read better or worse figures dependant on the rolling road. There are many other factors like higher tyre pressures on the driven wheels will tend to give better readings, however I hope the point is made.
It was once said that the meek shall inherit the Earth, I have since discovered that the meek don't want it.