Help for sizing a pfsense?

[Rampage]

hello everyone :)

i'm here to call for your help in sizing a server to run a pfsense.

here are the features i'm interested in and the size of my network:

i have
50 client in a LAN
10 servers in DMZ
2 internet connections i want to load balance ( 6mb/6mb and 3/512)
10 clients i want to run throught a captive portal
squid + squid guard for content filtering
layer 7 filtering

the features that are warrying me about hardware scaling are layer 7 filtering and squid-guard.
i'm not going to run persistent VPN, maybe there will be a client tunnel openVPN that will access the network for firewall mantainence.

the hardware configuration that i'm required to meet is:
4 gbit ethernet ports
considering that both the WAN interfaces are not that troughtput intensive i was planning to use an atom board like this: http://www.newegg.com/Product/Product.aspx?Item=N82E16816101332 with 4gb ram and a 2 port additional ethernet card.

i dunno how the traffic across the LAN and WAN is going to inpact on cpu usage and ram….

do you think it's going to be enaugh, or it's better to go for a core2 duo?