First show me your "optimum" speaker, source, amplification, etc.
The premise of the post is fallacious. :(
Anyone with experience knows that what you are asking for is not relevant to achieving the most pleasing sound with an audio system. Go ahead, procure measurements; they will bear little relation to whether you actually prefer the sound of a particular speaker cable. YMMV
BTW, leaving other cables out of the discussion ruins the entire endeavor. You cannot properly tune an audio system by placing focus only on the speaker cables. You may as well guess at it. :)