What speaker cable made a major difference in the sound quality of your speakers??

I am curious what speaker cables made a big "jaw dropping difference" in the sound quality of your current speakers.  What most impressed you about the difference;  that is, overall musicality, tighter, deeper bass, midrange clarity and soundstage depth, etc.etc. 

Keep the price of the speaker cables chosen or auditioned at  between $800- $1000 or  from  $1000-$1500. Was the cable bought new or used??

  Thank you,   SJ