I've ordered the Clark cable. As I said, it's not so much any improvement in sound I was after, I've been here long enough to know that lamp cable is as good as 'Audio-Snakest Titanium Plated Oxygen Free Pure Copper'. It was more to make sure that there would not be any problem with an 8 core cable.
Lamp cable is appealing, and I understand it's just as good as more expensive options, but I don't think it is the right solution in my situation. Each speaker would need 4 cables (tweeter, upper mid, lower mid and woofer) and I'm trying to make everything neater. If I can do that with a single cable and a SpeakOn connector without any negatives then it's what I will do.
I could have gone with lamp cable and a sleeve for it, but I've done that before with longer cables, and it's a complete PITA. I also think it would have been stiffer than the Clark.
I guess I should have titled the poll 'What should I make my 4-channel speaker cables from?'