Basic routing and switching - expect line speed. Don't expect analysis features to run at line speed - 30-50% penalty could be normal depending on throughput.

Stay away from IPS and complicated firewall rules which usually are done in CPU, and you should be fine. HW acceleration for those (esp. TLS decryption) is a major reason fancy firewalls are very expensive. You're better off building an IDS or picking up a smaller FortiGate or Palo Alto firewall if you really want to get serious there.