You mentioned you increased the RAM speed in the BIOS. Make sure you loaded the XMP profile, so that it changes the timings and voltage, rather than just increasing the frequency. Otherwise you're going to be unstable. It could be BSOD's, or it could just be drastically increased hard faults that impact performance.
Aside from that, I would use a tool like HWINFO64. Monitor your GPU power consumption, temperature and frequency. Compare the frequency against the base and boost frequency specified by the manufacturer. It should at minimum stay at the base clock. If it's dropping below that, it's throttling.
What brand and model is your card? It varies based on the cooler design. 82C sounds a little high, but it shouldn't result in throttling.
So when you buy RAM and I'm guessing your kit is 3600 C18 1.35v. That's the XMP profile. The JEDEC profile is probably 2133 C15 1.2V. So to hit that XMP profile and remain stable the manufacturer sets a profile that will increase the voltage and loosen the timings. In this case from C15 to C18. It's actually pretty impressive you weren't crashing running 3600 C15 at 1.2V.
That should be all you need to do. After that hit F10 to save and exit. You can use a program like CPU-Z: https://www.cpuid.com/softwares/cpu-z.html
Check the Memory/SPD tabs, it'll verify your frequency, timings and voltage.
Never tested the Suprim 3090. I did test the Suprim 3080 early on and it ran about 80C in a 75F environment for our testing. That's in a chassis. The 3090 running about 82C, depending on your ambient sounds about right. That card does have a dual BIOS setup. Make sure you're on the performance BIOS, not silent. It's a switch on the actual card.
Is there a way to switch to performance in BIOS or only this physical switch on the card? Do you think that would account for 2o-30 frame drop in some games? Trying to go slow here and only change things carefully.
By the way, thank you very much for the xmp profile point. Glad I double checked that!
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