Most distros compile their code for the generic 386 or x64 architecture. I was wondering for some time to what extent a certain processor benefits from a tuned compilation. For example compile a program with the flag -mtune=386, benchmark it and then do the same with -mtune=athlon-xp and compare the results.

If processor A gains 30% performance on average with a tuned compilation while processor B gains 15% that would skew the price/performance ratio in favor of processor A, that is, if you're willing to recompile packages for your processor.