I've owned also the Panasonic GT50 and still own the ST60. Now I own, the Panasonic FZ950 Oled and there are a lot of similarities but those similarities are enhanced by the Oled in my opinion. For lower SD resolutions nothing beats plasma but when you get into higher quality content 1080i/1080p with proper settings the Oled displays a better picture when comparing the 2. With 4K HDR is no contest. The Panny Oleds do an outstanding job with displaying a very accurate picture.
Media room- 65" Panasonic FZ950 OLED, Pioneer Elite VSX-90, Panasonic UBD-820 4K, Klipsch Gallery G28's, Klipsch Sub 12, Klipsch RS-52 II, Optik HD cable
Living room- Sony 4K 79XBRX900B, Onkyo RC-360,HTPC,Klipsch Reference R-62II,Rc52II,PS4
Gaming room -Panasonic ST60, PS3, Wii