below 100hz, do speaker cables matter?

I think it does. Especially if the woofer is inefficient. Heavier gauge speaker cable has less resistance. Longer runs require heavier gauge to minimize resistance. I recently tried Kimber Kable 8 PR for the bass modules of my VR-4JRs and the bass is deeper and better defined.

Bass notes have harmonic overtones that are directional. And the quality of cable certainly does make a difference both in the fundamental bass note and its harmonics, IME

Every time I've upgraded speaker cables the bass has improved as much as the mids and highs. I vote yes.