There is no such value configured in jvb.conf.
Then it uses the default, which I linked to. Note that the load reducer is not enabled by default.
I already repeated the tests with 8 CPUs. They show that it is not a problem with hitting the server capacity.
It’s maybe some serialization either from locking or explicit serialization in JVB code, or from GC, causing contention at higher packet rates. You could try running two JVBs on the same system and see if you can get better utilisation figures. We’ve generally found that on anything larger than 8C/16T, we need to run multiple JVBs (in VMs or containers) to make efficient use of the system resources.