Why? My logic is: if you would write an ideal "property accessor" library (or util class), what code would be the fastest

In that library, you would have to check for PHP 5.4 and fallback on reflection if PHP 5.3, so it's fair to have the benchmark include the test?

However maybe the test could be in the setup of the library (like in the constructor of the class reading private properties), so maybe indeed that's not fair to include it in the benchmark?