I got a 65" C8 to replace my 64F8500 6 months ago. I still regret it.
Yes, the C8 can easily be made eye-searingly bright compared to the F8500. No problem in the brightness department.
The other good thing is that the WebOS firmware is very nice and snappy, and the built-in applications are up-to-date and are still being updated.
Due to the sample-and-hold technology used by OLED panels, motion handling is just awful compared to plasma. Football is darn near unwatchable due to blurring. This can be somewhat mitigated by enabling black frame insertion, but this darkens the picture and somewhat over-saturates the colors.
Panel uniformity is a really big issue. Vertical banding is pretty much guaranteed (visible with a 5% grey slide), and various tinting issues are common. You might be lucky and get a panel that does not make the banding and tinting visible in normal source material (we were lucky in that respect), but many people are not so lucky: https://www.avsforum.com/forum/40-ol...ignetting.html
There is limited 4K source material available, and most people's eyes do not benefit from 4K anyway at normal viewing distances.
Up-scaling from 780p and 1080i is imperfect, and makes defects in the source (compression artifacts, etc.) much more noticeable.
There is so little HDR and Dolby Video material available that within a couple of months I had exhausted all there is that I am interested in watching.
I ask myself.... I spent a lot for money, for what?