I'm still skeptical about mains leads Marco, beyond any improvements made by just using thicker copper than the poor (thin) leads that are usually supplied.
I've seen some fairly outrageous leads (came in their own flight case and at a special show price of £1,700 off the asking price) plugged into kit and heard no difference at all, over a basic 25amp mains lead it replaced. So your not alone Macca, I wanted to hear a difference, but couldn't, if there was one, it was so small I didn't pick up on it and I'm sure that amount of money spent elsewhere in the system, would have a more noticeable effect on sound quality.
The automatic "Shielding must be good", just doesn't float for me. Unless you are using a separate grounding system for the shield and not your safety earth. All you are doing is collecting any interference using the very effective aerial the shield is and putting that interference into the safety earth circuit, which is connected to your case and probably used as the ground plane of your electronics. This might actually be worse than no shield at all, so I struggle with that one. Using a separate shield ground like a copper rod stuck in the ground etc, I can see how that might in principle, help prevent noise getting in.
Too many people have said they heard improvements for me to ignore the notion, I just haven't experienced it yet myself.