R6 is tiny case :- ) ? It's the best mid-tower case on market, it has fantastic airflow, you can even look up benchmarks for it (on GamerNexus, no one else does that kind of stuff). You can put 3 fans in front (2 front one bottom front) and open up the moduvent on top (opening up both slots helps with GPU, but hurts the CPU, opening only the second one helps both). Or you can keep the front open, or take out the dust filter.
The actual problem is more related to high-clocked RTX-Super cards and fans ramping up to 2000+ RPM very easily. You can only solve this by lowering the power limit so the card stay cooler at expense of some performance. It's not airflow starved.
https://www.tomshardware.com/reviews/nvidia-geforce-rtx-2080-super-turing-ray-tracing,6243-5.htmlMy 3950X also boosts mostly to 4.5/4.55 but that is kind of expected as it's marketed as "up to" and those are just spikes basically, for few seconds, it's not sustained boost. Some people are annoyed by this marketing but Intel now does it as well with "Velocity Boost clocks".
4.1-4.3Ghz all-core boost on other hand is more than advertised and just great.
There is one aspect to Zen architecture and that's stress on memory controller being inverse to CPU. So high-clocked memory will inadvertly take down a bit of single-core boost. It's possible to stay at lower memory frequency but with faster timings to get around this. But it all makes absolutely no difference in the end, none of it is perceptible difference in performance.
For higher performance, there are Threadrippers.