Hi
You will find that it is down to the rolling road lottery.
Sorry if you have a 150PD then that is what you will have.
The machinery now days that are used to produce the engines are spot on so if you have a 150bhp car as standard then that is what you have.
The rolling roads are something else they can produce different readings.
If you have an optimistic rolling road to start with , if you have it remaped after it could look like you have 20bhp over and above what you should have.
With that in mind you can see why some have them quoting over
Sarah