Unfortunately, I often note that there is a huge gap in understanding of network performance testing methodology.
Almost every related case goes down to “It seems it was quite better earlier”. No metrics, no anamnesis, so it makes me sad each time.

Just to be more confident I’ve gone through these canonical documents. Will keep it in mind for reference.

ITU-T Y.1564: Ethernet service activation test methodology
RFC:2544: Benchmarking Methodology for Network Interconnect Devices