Nice read

One observation though - when it comes to actual performance in a game, there is a difference between stand-alone benchmarks and different portions of the game, thus sustaining your point. However, when it comes to the % diference of performance between 5850 and GTX 470 (your examples) I see almost not percentage difference between the two from one situation to the other.

The point is very simple, based on your tests and results - if real-life performance in a game is what you are after, then in-game testing, even if it is far less accurate then benchmarks due to a large number or variables, is the way to go. However, if accurate performance percentage difference between 1,2,3, etc products is what you are after, benchmarks are in no way less representative then in-game testing.