Lots of problems here:
This is only for MyISAM tables. If you have no MyISAM tables, remove this parameter and all other Key_* params.
Unless you have 20,000 connections on a regular basis, remove this and Thread_pool_size. Thread pooling is only beneficial when you have massive amount of connections.
Remove these as these place limits on parallel replication
This should be 0 unless you are facing CPU/context issues.
This parameter is wrong. There are many blog posts on why increasing this value can have BAD performance. Please change this to 800.
Make the above changes and restart MySQL.
Or the last option, migrate the database to mysql enterprise (mysql oracle)
Because Percona is a rebase of MySQL-Oracle, you will find the same behavior. There is no reason to switch to Enterprise, unless you like paying more $$$ for MySQL.