Series of tests where I try DOOM Eternal on Ultra settings, 1440p, with DLSS and RT on, and changing the pcie socket from the PCIe 5.0 x16 and PCIe 3.0 x4 to simulate performance as if it was an eGPU via a thunderbolt 3 dock. I also tried other codecs for the video, since this one the original has ~4GB in size, and the recoded ones 470MB
This video is another original one without recoding, on the PCIe 3.0 x4 slot on my pc, you can see a dip in performance but it's not linear to the PCIe bandwith (~64GB/s to ~8GB/s) since it goes from ~90 to ~60FPS, plus the metrics from in-game shows that the real bottleneck is in the cpu from the cut pcie lanes connecting the gpu, proving that NVIDIa cards aren´t much pcie dependant, this in an extreme, but from pcie 4.0 to 3.0 x16 shouln't be an issue, since most of the gpu logic operations run inside the gpu, it barely comunicates with ram and cpu