Difference depends very much on actual workload. For example, I have a small server with mostly CPU-bound programs running, where the mitigations do not noticea

Difference depends very much on actual workload. For example, I have a small server with mostly CPU-bound programs running, where the mitigations do not noticeably slow down anything, but a simple "xz -l large_iso_file" takes 20 minutes without mitigations=off, but only 2 minutes with.