Pretty dang close, propagation delay is often given as a percentage of the speed of light (c). Here's a fun table with a comparison a few pages into this PDF:

Pretty dang close, propagation delay is often given as a percentage of the speed of light (c). Here's a fun table with a comparison a few pages into this PDF: https://www.commscope.com/globalassets/digizuite/2799-latency-in-optical-fiber-systems-wp-111432-en.pdf?r=1 https://www.commscope.com/globalassets/digizuite/2799-latenc... It's all about the dielectric constant of the propagation medium. If you're building a system with copper for PCIe gen6, which is 64Gbps PAM-4, you're probably using something like Isola MT77 or Tachyon with Dk around 3.2 and very low dielectric loss. That being said though, I believe the signal attenuation in a FO system would be far better than copper interconnects.