Yes, absolutely. I will answer this a bit differently from some others. I, like you, still love my Panasonic plasma (GT 50). But I actually get a slight boost from my current OPPO 203 (just purchased the Panasonic 820 for another Panny plasma). Your question was the same as mine before my purchase. I wanted to “sort of” test out the new 4K players, and still continue another year with our gorgeous plasma...there is not too much difference as of course the 1080p is, well, still 1080p, BUT...when I hit “info button” there is DOUBLE TO TRIPLE the bit rate coming off that 4K disc from the 4K player, and it serves up about 60-80 mkbps (sp?), as compared to 2K Blu-ray of about 20-25. It DOES maximize your plasma out !
So the long & short is YES. My Panasonic tv (GT50) accepts a 4K HDMI cable that OPPO supplied. For the Penny 820, I think you will need to purchase a new HDMI cable to send the beefed-up signal to the TV. I recommend only the “Premium Certified” HDMI. A GREAT source is ”MONOCABLE.” They are an on-line business that have impeccable quality at a fraction of cost- great combo !
Best wishes. Let us know how you did !