I have an all Harmonic Technology system right now. Pro-9 Plus speaker cables and Pro-Silway Mk II interconnects. I really haven't done much A/B testing with the speaker cables, but I did a little with the interconnects and found the Pro-Silway's made a significant improvement over my former HT Truth Link's. It's really hard to say which is the more important link. Both are an important part of the total system. I'd say start shopping the used market and just buy whatever you find first at a good price. Used gear has the advantage of already being broken in for you.
Greatest sonic impact: cables or ICs
I have reasonable equipment (thiel and classe) and am looking at upgrading my speaker cables (20 ft audioquest type 4) and interconnects (musical concept superconnects). However, the cost can quickly get out of hand. Which has the greater impact on sound speaker cables or interconnects?