Doctor John, as far as this: John, you mentioned Earl Scruggs tuning his banjo sharper to give it a brighter sound but is'nt this because the strings are tighter rather than just of a higher pitch?--you can't really separate the two. The three ways to raise a given string's pitch are to make it shorter, thinner, or tighter--and if you do make it shorter, thinner, or tighter it WILL raise the pitch. When a string is installed on a banjo, there's no feasible way to make it shorter (leaving aside fretting it for the purpose of this discussion) or thinner, therefore you cannot make it higher pitched without tightening it and you cannot make it tighter without raising the pitch.

Now, if I understand you, this: If you play a guitar just above the bridge it will have a very different sound to playing it much higher (=higher up!) even though the pitch is the same.--refers to where, along the length of the instrument, you strum or pick it. And yes, it's true that there will be a noticeable difference to the sound, but that is quite a separate issue from that raised in your first sentence.

By the way, did this thread manage to answer your original question to your satisfaction?