Power Cords

I currently have Wireworld Silver Electra power cords with upgraded Platinum plugs. I had two 1M Wireworld Platinum power cords, but rearranged my system and required longer cords. Yesterday I borrowed two Shunyata Sigma NR power cords. On the first note my wife softly said, "that sounds better". She said it was clearer. I listened for a couple hours, changing the power cords a couple of times. In my system and to my ears this is my conclusion:
The Sigma's are cleaner, definitely has more bass, a dead silent and completely black background. The Wireworld cords are more detailed, with a wider soundstage and better spacing/separation of instruments. All things considered I'll keep my Wireworld, but I'm curious to listen to other power cords.
After inserting the Sigma's I just don't understand how anyone that listened to different power cords could conclude that they can't hear a difference. There is a difference, but like any other component the individual has to decide if the change is worth it. $6K for two power cords is relatively expensive. Expensive, but oddly maybe a good value? In my system there was a definite improvement with better bass impact and articulation. Would spending $6K or just changing amplifiers yield similar results? As with most components there are trade-offs...is there a power cord out there that has the benefits of the Sigma's and Wireworld Silver Electra's? If so, at what cost?