I can't help you on the speaker cable.
I did upgrade from a Venustas tonearm cable to a Proteus Provectus tonearm cable. 1st is much blacker background and resolution goes up, distortion goes down. It's a more articulate cable. 2nd the normal fluid vs ferrox differences found in Dominus seem not to be there. good extention at both extremes (better than venustas) and a glorius midband. For me in this application, it's a complete upgrade, nothing suffered.
I did upgrade from a Venustas tonearm cable to a Proteus Provectus tonearm cable. 1st is much blacker background and resolution goes up, distortion goes down. It's a more articulate cable. 2nd the normal fluid vs ferrox differences found in Dominus seem not to be there. good extention at both extremes (better than venustas) and a glorius midband. For me in this application, it's a complete upgrade, nothing suffered.