I've been thinking of replacing my aging OPPO-103 and was torn between the two Panasonics you mentioned, the DP-U9000 and the DP-U820 and will most likely go for the DP-U9000.
From what I've read, both have fans and the one on the U820 can be heard on quiet scenes from a distance of about 8' and the image quality is marginally better on the U9000. The U9000 is also built like a tank, just like an OPPO. That would do it for me. Also, both Pannys automatically switch to Dolby (if available) so no need to go into the menu to select what's optimal for each disc you choose to play.
Good luck in your decision. By the way, what is the price you found, if you can reveal it?
All the best,
Nonoise