The task of selecting a stateful firewall that meets the performance needs of your network environment involves correctly understanding a set of parameters that go beyond the classic perception “the more Gbps, the better”. As a matter of fact, when taken alone, the Gbps number may be quite misleading for the evaluation of any stateful element. This happens because a network device that cares about state, forwards packets as part of connections and not on an individual basis (as routers and switches do).
More details about this important topic can be found in the following article that I wrote for the Cisco Support Community:
Revisiting Firewall Performance Parameters [ https://supportforums.cisco.com/docs/DOC-16954 ]