I'd guess the bespoke hw is not necessarily faster signaling, but rather functionality. E.g. fast multipath routing in a Clos fabric, firewalling, maybe offloading some specific workload (IIRC ms was using fpgas to offload some aspect of search for Bing)

Going back to signaling, AFAIU the state of the art is 25 Gb/s per lane, 100 Gb networking aggregates 4 of those. 50 Gb/s is still in the labs.