HW firewall for LAN

["Dan Duplito" <danduplito () techie com>]

hi, forgive me if this is a newbie query -- i'm relatively new to the security industry.

we're looking to getting a HW firewall between our LAN and internal servers, similar to the one we have for our DMZ.

i'm just wondering if a Cisco PIX (515 or 525) firewall is not overkill for a 3000+ user-base LAN/WAN network (i've 
read the specs from Cisco site but nothing was mentioned regarding user-base limit/capacity for each firewall). traffic 
will mostly constitute the usual Internet, mail, dns and telnet/ssh access to the servers. 

is there a rule-of-thumb for determining the appropriate firewall CPU speed and memory for a particular number of users?

TIA for the help and inputs,
dan

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