As in most high end audio, it depends. From my experience (50 years) in general speaker cables, power cords, and interconnects. But they are all important and there are many exceptions.
To really get a handle on the sound characteristics and to optimize your system.
First complete your component upgrades… making sure you are completely happy and sure all major components are complimentary and sound great. I use my budget / standard wires: DHLabs. They are good quality and relatively inexpensive… they are my standard for reference.
I get my system broken in… say 500 hours. Based on the sound I will try a few high end speaker, generally Cardas, Transparent, Nordost, WireWorld. I very slowly rotate… a week at least. Listening to music not the equipment. Then amp power cord (AudioQuest Storm Series), then interconnects… and finally power cords to the rest of the system. The process can take over a year… but at the end I have complete confidence in the sound I have. There has been no guess work. I know exactly what each cable has done.
It has taken thirty or fourth years to get this down. It is too easy to be in a hurry to get things over with and make decisions.