Help me, I am new to STI.

When replacing the cables should I get the non-stretch ones from
Aztec?

With my Dura Ace STI the chain clanks lightly when I am in big ring
and middle cog. It is adjusted properly for the limits. A knowledgable
friend recommended replacing the cables etc
I am looking at replacing the cassette, chain, and cables. Is this
all worthwhile?