> the temperature differance is significant and the metal strings will contract

This is the piece of folklore that I've always heard but never seen real info about. If this is going to chellenage my guitar significantly then I should think very seriously before getting a pickup mounted (they'll have to take the strings off which is about as challenging as things get, and the 'lore' that says change one string at a time is still at the back of my head from the sixties). Also I have the problem that it can get down to quite a few degrees below zero outside (we're talking Norway here): how cold must it get before I should forget going to the Tuesday session because my guitar might not get there in one piece?

-mike-