That i7 comes in on Passmark about 8,200, vs the E3-1240 v2 around 9,200. It really depends on what you're using it for. Simple home traffic - either one would more than accomplish the purpose & then some with just a pfSense firewall running. In fact either of them running just pfSense would be overkill.
For comparison, I run an entire Sophos UTM 9 platform - firewall, IPS, web filtering, SMTP & POP3 proxies, endpoint protection for 9 boxes, dual antivirus (Avira and Sophos), antispyware and antispam - on a R210 II E3-1280 v2 with 32GB servicing a 2 link load balanced 800/800 WAN and that's overkill. (which brings up another question - why just a firewall vs unified threat management?)
Frankly, you could run just pfSense acting as a firewall on most home connections with a Pentium 4 & 4GB. We set up my next door neighbor's installation on an old Sun UltraSparc box he had lying around and it's bored most of the time. I ran it as a test case (to establish a benchmark) on my WAN setup for a week or so on an old Optiplex Core 2 Duo desktop with 4GB and it wasn't really stressed. pfSense is not exceptionally resource intensive.