Z490 boards do support pcie 4.0, but current intel 10gen processors and bellow doesnt not support pcie 4.0, however rocket lake cpus, that is, 11gen processors that should drop by first half 2021 will support pcie 4.0, so if by some miracle pcie 4.0 proves to be faster somehow right out of bat you can still upgrade to gen 11, but as said just above, right now pcie 4.0 is like trying to make your car go faster by installing a bigger fuel tank, nothing so far can fully saturate the current pcie 4.0 lanes, not even at 4k. Perhaps indeed at 8k at high hertz but thats not really a thing atm... especially when 1080p is still the majority and so the standard, and we're just starting to see more and more 1440p, let alone 4k