it honestly depends what gpu youre using considering the bandwith difference between most pcie gens if you have the best next gen gpu and use it to its fullest its gonna be much faster. Thats why theyre making the new generations because as gpus get faster and process more data at a given time you need more bandwidth to make sure youre not bottlenecked. but if you mean should you upgrade to a pcie 4.0 motherboard because youre getting a 30 series card you dont need to as you can see here https://www.extremetech.com/gaming/314627-nvidia-ampere-rtx-gpu-pcie#:~:text=You might also be happy,slots wouldn't cut it.