What hardware spec would I need to push 20 gigabit of network traffic on an OpenBSD server?

[Some Developer]

I'm just wondering what hardware spec I'd need push 20 gigabits of 
network traffic on an OpenBSD server?

The planned configuration is to have 2 10GbE network adaptors and have a 
10 gigabit incoming network connection and 10 gigabit outgoing network 
connection (incoming will be an L2TP tunnel and outgoing will just be 
forwarded on to the internet at large).

The thing is I want to log all traffic on the server for that so I'm not 
sure how that will affect performance of the server. Obviously I'll need 
a large storage pool to store the data but I'll use syslog to write to 
an external logging server which will then save the logging data to a 
large SAN of some description.

I'm just wondering a) which 10 gig ethernet cards I should buy, b) what 
CPU would be required and c) how much RAM would be required.

Basically the only incoming traffic would be L2TP authenticated via 
RADIUS and outgoing would just be the forwarded traffic. Other than 
logging I doubt I'll have very complex PF firewall rules at all. I don't 
know much about it but from what I have read it sounds like I'll also be 
making use of CARP as well for multiple servers.

Thanks for any help.