@losepete Hi Pete: Contact Chris at VH Audio, he has what you're looking for.
https://www.vhaudio.com/wire.html
Consider his OCC solid core with special AirLok insulation which has the lowest dielectric constant.
His V-Twist is excellent which I have recently used to rewire my amp from input to amp module. A big improvement over the previous stuff.
The quality of wire makes a big difference but, in my opinion the quality of the RCA connector is even more important. He also sells the outstanding range of KLE Harmony low-mass RCA's
The Copper Harmony pack of 4 sells for $51.99 which is crazy good value. I am slowly replacing all my RCA's with these or the top of the range Absolute Harmony. Easy to work with.
WBT also has very good units at much higher price.