Not meaning to hijack this thread. Just wanted to pitch in to this great community.
i3/i5 system is not going to suck up $20/month of power. More like $2 o r$2.5 (use PowerD !!) even if you keep hammering the router with 30+ users. That's about $24 to $25 a year. Still cheaper than the under powered Atom junk.
I used an i3 system for 6 months and now using i5 with 8GB RAM since past 3 months.. Haven't noticed much of a change in my electric bill. Keeping in mind I have now close to 50 network hungry bulldog users, dual WAN 100/16Mbps (50/8Mbps each) internet, 4 VLANs and network is hogged up 80% or more 24/7. Also to add on top of that, I am running Snort on both WANs, HAVP, Squid, SquidGuard & LightSquid.
All this is in a small Thermaltake enclosure.
Of course you don't need or want this. But keep in mind that later on if you don't need pfSense to run on it, you can turn it into a full blown desktop or Hackintosh.