Yes it's overkill and more power but it gives me more options

For sure it will! You will be able to run all packages you want and with a sufficient
SSD drive this will be a really hardcore pfSense box! You can be;

• under performed = nothing goes
• right performed = all goes but with small or no headroom
• over performed = likes "right performed" but for a longer time of usage

What's a good Intel quad NIC? I see a lot on eBay, some Dell branded, etc.

Intel NICs would be the best choice!
$18.99 Intel i350-T4

What's a good Intel quad NIC? I see a lot on eBay, some Dell branded, etc.

Looking some opinions on the following two systems. I have an extra Supermicro X9SCM-F-O motherboard that I had planned to pair with a Celeron G1620 temporarily until Skylake Xeons come out and then I'll pass down my Xeon E3-1220 (Sandy Bridge).

At these days nothing beats an Intel Xeon CPU! But it is also sucking much power and only for 15 users
it would perhaps to much power usage, but compared to all other CPUs the Xeon is a real king!

However, I've noticed the new Atom boards are very popular and have 4 port NIC built in.
I'm considering selling the Xeon and X9 board and getting an Atom. Probably the A1SAM-2550F-O.

I would more like to go with the SUPERMICRO A1SRI-2758F (C2758) if you want to go by the mini ITX format
and a SC101i or M350 case, but if you are looking more for a 1U appliance I would have a closer look at the
Supermicro A1SRM-LN7F-2758 (C2758) with 7 GB LAN Ports and a mSATA slot on board!

Looking for some input on what to do.

Than let us talk at first about your budget please.

My internet is only 100/10 cable but want to be ready for gigabit when it's available.

All named boards above are able to serve this line.

I don't know anything about packages but I see Snort and Squid mentioned a lot. I want enough headroom to run anything I want.

Than perhaps the Atom C2758 instead of the C2750 platform?

This is for my home, probably max of 10-15 clients at any given time.
Either way, chassis will likely be a 2U Norco and 430 watt PSU I already have.

To much power consuming, not the system itself but the electric power consuming is the point.

This server will be bare metal with the sole purpose for running pfsense.
Right now plan to use my existing 48 port HP 1910 switch and convert my Apple AirPort Extreme to wireless access point.

Ok then the Supermicro boards are fitting really good, otherwise the pfSense store offers also SG-xxxx units
that comes with 3 miniPCIe slots for modem, WiFi and mSATA cards that could also fits your needs.

I know the Xeon is about 4 times faster overall but it also uses more power and I'd have to add a NIC.

For sure but a used Intel Quad GB LAN Port card is only at ~$60 and the Xeon is a real king, nothing
betas him, as I see it right. Capable to do all you want.

The E3-1220 is total overkill, total….