QUOTE(flagstar @ Mar 23 2019, 05:31 PM)
After some thorough testing (not undervolt the card yet) with just the front panel open and fan filter above the case removed(I now had time to test this seriously), it seems @stevelum7 and @1024kbps were right after all, it is my problematic case and case fans itself. With those front panel open, my gc clock speed maintain at 1755MHz max 80c temp. If it were temp throttling, it would just sit below 1700MHz. Fan speed is set to auto at this point.
When I set the fan speed to 100% (front panel open), it would drop the temp further to sweet 73c 1770MHz, with quite audible fan noise from gc.
Afterwards, I tried to undervolt with the help from Afterburner to 1818MHz @ 950mV. It didn't change much however, sitting well averaging 78~80c at 1755~1770MHz. I would try to undervolt further if I could later on.
It was on auto, when I run it with closed case.. fan spin around 82% when temp limit were hit. It's audible but not that loud.
But since the front panel can't be completely removed you have to put the front panel at the side every time you play game? That will make inside your casing full of dust.
Have you tried remove side panel (without removing front panel) and see if the temp drop?
The main problem with your setup are that AMD fan blowing air into heatsink, which afterward the hot air is spread out on the whole casing. The front fan blowing to motherboard while AMD fan blowing out of motherboard, it create resistance. The RTX also making it worse by spreading the hot air everywhere. One way is to change the heatsink to the type that have the fan blowing to the back of case like this:

But you still need to remove the front panel to have better airflow.
If the temp drop when side panel removed, I have an idea how to improve the airflow without spending any money. Can the side panel transparent acrylic be removed? If can (Or you willing to remove it by force), install a filter (pantyhose work like magic) after remove the transparent acrylic and reverse the front panel fans so that it suck out air. Now the hot air that's being blown everywhere will be suck out on the 3 sides of the case while the side panel letting cold air in.
Letting the GPU fan spin faster is not a good idea, it shorten the fan lifespan. It would be better to have the case fans spin faster instead to have better airflow as it would be cheaper and easier to replace. Can all the 4 fans speed be controlled? Because it can get very loud when all 4 fans spin at max speed so it would be better to have it spin at max speed only when gaming.