I say you can tell the difference between cables but as with all hi-fi its diminishing returns and has to be kept in perspective.

I COULD tell the difference when the left speaker was wired with different cable to the right. I didn't buy enough cable to complete the job properly. Both 'Budget' cables, but sounded different. Not radically, but I could certainly tell and was much happier when it was nicely balanced with the same type of cable.