I believe the answer to be "none". It doesn't matter a bit, unless you are planning on upgrading all of the Romex in your walls as well with $500 a foot cord, how would upgrading the last 3 feet matter at all?
Another point, if your amplifier is properly designed, it will have capacitive reserves that more than make up for the types of effects spoken of in the above posts.
Another point, if your amplifier is properly designed, it will have capacitive reserves that more than make up for the types of effects spoken of in the above posts.