The untwisted ribbon cable is fine for PCIe in short runs by virtue of PCIe data lines being a differential signal and if the length of cable is kept short(-ish

The untwisted ribbon cable is fine for PCIe in short runs by virtue of PCIe data lines being a differential signal and if the length of cable is kept short(-ish). The max length of the cable should vary inversely with the generation, that is, max length of a flexible copper extender for gen v1 is longer than gen v3, more length introduces more noise which increases error rates. A well terminated cable should be able to use the full bandwidth of the bus. I'd be completely comfortable running x16 flat out at max rate with one of those. I don't have any hard-and-fast sources to back the above up, but punching 'pcie extender max length' into the Gargler should find you something to suffice.