samtec has an obscene JTAG cable assembly (via @G_glop)
i think the moment you start rating your JTAG connector at "7 dB insertion loss", something has went very, very... strange
this looks like a shitpost i would make about JTAG except it's inexplicably real https://suddendocs.samtec.com/catalog_english/hhsc.pdf
people say things like "breadboards are 10 MHz max" (basically true) from which they derive conclusions like "pin headers, which have the same pitch as a breadboard, are 10 MHz max" which are entirely false. although you do need to treat it like a transmission line above ~20 MHz or nothing will work
@whitequark
Nokia used to push 900 - 1000MHz through long pin headers in the TMN-1 NMT900 mobile phone.
And a few other places, but that's the highest frequency I have seen.
Others are <500MHz.
@ftg @whitequark USB 3.0 front panel connectors on PC cases use a 2.0mm pin header to connect to the main board, so that gives your 5GBit/s: https://www.intel.com/content/dam/doc/technical-specification/usb3-internal-connector-cable-specification.pdf