This is the official xmrig benchmark site, all tests there are done online and validated on the server. What you see in the table at the top is an overclocked and highly tuned CPU (i.e. consider it competitive benchmarking), probably water cooled and with tweaked memory. 18-19 kh/s for 5950X is actually low, it can easily do 20-21 kh/s with just a bit of tuning.