Slow speaker cables?

As Almarg and Jcharvet have alluded to, I judge a cables speed, fast or slow, depending on how it attacks a note and releases it (decay). Attack and decay are the primary contributers to the timbre of a musical instrument. Attack is how clear is the leading edge and decay is how long the note takes to dissipate.

Some cables attack and release a note quickly and move on to the next note, these cables tend to be called fast, revealing, articulate or transparent, etc. Other cables tend to hold on to a note longer, allowing it to resonate or decay longer, these cables tend to be called slow, warm, musical, vibrant, etc.
It doesn't have to do with the musical timing of the instruments themselves, but how the notes that they play resonate, which determines how the timbre of the instrument is perceived.

12-12-12: B_limo
I'm also thinking that, just like some people can break down all the qualities of a particular wine (not me by the way), others are better at picking up on all of these nuances of audio qualities.

I'm not much of a wine connoisseur either. However, I have a few friends that are, and just like in picking up audio nuances, most connoisseur's learn from training their senses, they are not born with a gift. I've learned to listen with a ear trained over the decades of listening. It's more about learning what to listen for, this just takes time and experience.

Why is it that with some cables I am barely able to hear instruments in the background that with other cables just get muddled up? Is it because they are "faster", i.e. quicker attack and less decay resulting in more space between notes resulting in better definition and less congestion within a certain piece of music? If so, then why also can I hear certain instruments better even if they are overlapping other instruments? Less distortion?

This is hard to answer, it could have something to do with more speed and resolution, with faster attack and decay it leaves more silence between the notes to hear other sounds. However, it also could have something to do with the cables soundstaging ability. Some cables are more 3 dimensional with a deeper soundstage, while some have a larger, but a flatter, more 2 dimensional stage. Sometimes cables with a flatter stage can make background sounds appear more immediate, or clearer. I still prefer cables that have a deeper soundstage, some might call it the mid-hall perspective. However, I know others who prefer that feeling of sitting in the front row. You pay your money, you make your choices.