Prior to me having the Siltech Firewire (3yrs ago), have always listened to my 6yrs old dCS stack in their up-sampled mode of 44.1->176.4/192 (via Siltech double AESBUs). Yes, better Firewire cables do make significant differences so much so that I found myself now preferring/listening in their 44.1->DSD up-sampled mode almost exclusively.
I added the 2 x Siltech FW-6 classic mkII replacing the standards much later as I too was initially skeptical for same reason some mentioned above, but listening is believing. My only regret is that I should have done it sooner.