The very best plug wires from a conductance perspective are multi-strand copper wires.
From a RFI perspective, solid core wires will act as broadcast antenna transmitting the ringing voltages to other wires.
The insulating propertiy of plug wires is quite important, possibly equally important to low resistance wires.
But where does the RFI originate? We have used copper mesh shielded wires, grounded wires, and all sorts of "trick" wires.
The RFI comes from ringing voltages created when the firing voltage drops at an air gap. Where are the air gaps? At each spark plug and at the distributor cap rotor/post gap. High resistance connectors at each end of the plug wire will dampen the ringing. Ringing can be determined by holding a scope probe at various points along the secondary wire path.
Or, bag the whole problem and go to a coil over plug system.