Though for the most the performance cost of going down to 8x PCIe is often pretty tiny - only a couple of percent at most [0] shows a pretty "worst case" impac

Though for the most the performance cost of going down to 8x PCIe is often pretty tiny - only a couple of percent at most [0] shows a pretty "worst case" impact of 1-4% - that's on the absolute highest-end card possible (a geforce 5090) and pushing it down to 16x PCIe3.0. A lower end card would likely show an even smaller difference. They even showed zero impact from 16xPCIe4.0, which is the same bandwidth as 8x of the PCIe5.0 lanes supported on X870E boards like you mentioned. Though if you're not on a gaming use case and know you're already PCIe limited it could be larger - but people who have that sort of use case likely already know what to look for, and have systems tuned to that use case more than "generic consumer gamer board" [0] https://gamersnexus.net/gpus/nvidia-rtx-5090-pcie-50-vs-40-vs-30-x16-scaling-benchmarks https://gamersnexus.net/gpus/nvidia-rtx-5090-pcie-50-vs-40-v...