Plasma owners rarely accept any LCD and even OLED as same or better. You have a Rolls Royce HDTV so you'll be very hard to please.

Cable content can also be 1080i or lower so scaling that to 4K may do nothing more than amplify the visual defects in the source.

Again, OLED should have a fair shot at war with the plasma but due to how plasma works, you may not like OLED. You are doing the right thing of testing and returning products that don't meet your requirements.

Be sure to call in on each new model to be sure the firmware is current as well to chat about upscale failures.