Is there really a difference between SATA II and SATA III cables? And does it matter for normal spinners which cable to use?

No difference that I know of.  But always buy the best quality SATA cables, at the best price you can find.  Monoprice is the favorite source for many of us, and they are now on Amazon.

http://www.pcgamer.com/is-your-sata-cable-slowing-down-your-data-transfers-max-pc-investigates/

 

"There is virtually no difference between a brand-new SATA 6Gb/s marked cable made this year and one produced nearly eight years ago as far as performance goes. Expensive cable, cheap cable; long cable, short cable—none of it seemingly made a real difference."

"There is virtually no difference between a brand-new SATA 6Gb/s marked cable made this year and one produced nearly eight years ago as far as performance goes. Expensive cable, cheap cable; long cable, short cable—none of it seemingly made a real difference."

I'd agree given some conditions. The initial fresh connections should all be identical in performance, it's pretty much just a simple set of wires from point a to point b.

 

Some cables can stay connected better over time, because some cables can be more resistant to outside influences, strain or vibrations. SATA push on connections are very poorly designed when it comes to retention, so any help you can give them to keep them squarely in place is good.

 

I leave it to the reader to determine whether or not  any specific cable feature will help long term connection quality. It's not a one size fits all answer.