In this case you'd want to discover a network bottleneck by looking at network utilization directly using a command like `sar ­n DEV 1`. (from http://www.brendangregg.com/Articles/Netflix_Linux_Perf_Anal... )

It's generally possible to go 3x-10x faster than Linux if you make some tradeoffs like dedicating cores to polling. See https://www.usenix.org/node/186147 and https://wiki.fd.io/view/VPP/What_is_VPP%3F Moore's Law excuses a lot of sins, however, so on the latest servers Linux is probably adequate up to 100 Gbps for most use cases.