I don't believe I've ever run across a section of the PCIe standard dictating cable or PCB trace length requirements. All I've ever seen are signal integrity re

I don't believe I've ever run across a section of the PCIe standard dictating cable or PCB trace length requirements. All I've ever seen are signal integrity requirements (ie. dB loss) and timing requirements. The timing requirements are not tight enough to preclude long cables, and while the signal loss requirements are chosen based on what's practical and affordable to achieve with a PCB, they don't directly concern themselves with setting minimum or maximum reach lengths.