[citation][nom]JackFrost860[/nom]how dos a change to driver code improve the performance of one video game over another and what do these changes do to existing games that are many years old like the original Far Cry (yes i still like to play it once in a while)?[/citation]
This is a rule of thumb so not an exact science but...
New drivers affect new games as they tweak specific settings to allow the game run smoother as the driver includes profiles for a massive list of games so it is these profiles that are tweaked, not the actual drivers or software.
When a new series of GPUs are released then the drivers and the game profiles are tweaked by new driver releases. However, this will only improve for the vast majority only for the first couple of new drivers releases after that the new line of GPUs. After this things settle down and again it is more down to profile tweaks for individual games.
As for old games... if you have one of a new GPU line then you may notice a few improvements for the first couple of driver releases. If you have an older GPU and are playing an older game then you will most likely not get any performance benefits from newer drivers.