TLDR:
It’s only about a 6% perf drop on Intel machines. AMD systems and Intel 9900KS are hit less but no far one one’s done an aggregate of patches go get exact numbers.
Security patches on processors in the past year took performance down a bit. Most reviewers don’t consider these when benchmarking or only benchmark 1 patch at a time. Here’s a person who took time to benchmark them altogether with results.
Setup - 6700K 4.5Ghz/3.3Ghz RAM with mem tweaks/Windoze 1903
https://imgur.com/a/GUvDDB6
Benchmarks:
https://docs.google.com/spreadsheets/d/e/2PACX-1vQyoUJfh7i3RtWqbMvhNMsecNCIdT3NM41-VRAwRCzEQpIrlYtyQPA8X2il7Wnm_BN50kvS06oheMN_/pubhtml#
If memory serves me right Intel 9900KS has some of the security fixes in hardware and performance should be slightly better (Stepping D Revision 0).
Edit: Courtesy of by