Open to suggestions there. It's a fairly complicated topic though, hard to boil it down to a simple table these days.
You also have to consider pps, packet size, the NICs being used, etc.
The table is just a general guide but it could use a couple of intermediate steps (Such as ~400 Mbps can be done on an Atom)
If anyone has some solid data – from actual pfSense installs -- of throughput achieved and the circumstances (cpu type, nic, packet size, pps/bps) it would help.
Seeing a FreeBSD or Linux benchmark on the hardware isn't very useful of course, it would need to be data from traffic passing through pfSense.
Bonus points for VPN speed with several different ciphers. (As in http://forum.pfsense.org/index.php/topic,27780.0.html )