No more than about 5 percent. My experience is that money is typically better spent on the actual components and speakers than on cables and tweaks. YMMV.
BTW, @noromance - What are "NOS Belkin interconnects"? Are they made with a certain type of commonly available cable such as Mogami or Belden? Also, I agree with you about "solid core...wire" sounding best for speaker cable. My three favorites here (Cardas, Harmonic Tech, and DIY Jupiter wire) are all solid core.