hi behonest m8 ive never noticed a difference i just replace mine on my 360 but thats only because i needed a longer one amazon do one for about £6 thats the one i got it says its for the 360 but im pretty sure they are all the same type of connection.
Nope - same deal as HDMI. Its a digital signal path so won't make a difference.
I have a £3 delivered one from Ebay, and it has lovely 'gold plated connections' and 'polished fiber optics' whilst being 'double shielded' if it makes you feel better.