Phoronix published The Mitigation Impact Difference On AMD Ryzen 9 3900X vs. Intel Core i9 9900K Performance A quote from the article:

Last week I shared benchmark results of the AMD Ryzen 9 3900X vs. Intel Core i9 9900K in 400+ benchmarks in the largest comparison ever for these two competing ~$500 USD processors. If that wasn't enough, I repeated the hundreds of CPU/system benchmarks again but without any of the recent CPU security mitigations in place to see how the situation would have played out pre-2018.

  The Mitigation Impact Difference On AMD Ryzen 9 3900X vs. Intel Core i9 9900K Performance