Thank you for an advice. Just checked the specifications, and even these are expensive connectors, there is no pure copper, as : Main conductor: for Furutech: Nonmagnetic Rhodium-plated α (Alpha)Phosphor bronze conductor; for Eidolic - copper alloy (I’m reckoning that would be brass then?) plug chassis, layer of rhodium.
So for above mentioned alloys we have (if electrical conductivity of Copper is 100%): 11% for Phospor Bronze, 28% for typical brass, 38,40% for Rhodium. Unfortunately, even the Aluminium has 61% of Copper's conductivity.