A Single Board Computer as a home network server?

Hi spoon, welcome to the party.

From the sound of it, you have the issues and tradeoffs well in hand already, so we may not be able to add much.  I can't quite make out the level of performance you're looking for, as you seem to be giving consideration to everything from BeagleBone Black to a Core i3 board --- that's a very large range of performance!  What's more, the range of prices you've mentioned is also very large, to make the choice even more complicated.

What I can recommend stems from the fact that you've identified that "The file sharing and proxy server may be a little i/o and network intensive at times."  That's going to be your main constraining requirement then, because ARM boards are a bit lackluster on I/O.  (PCIe in particular is as rare as hens' teeth on ARM.)  We've done a lot of measurements on "SBC Network Throughput" (the title of our corresponding thread), so you might want to glance at that first.  As that table will show you, not all ARM boards will fully use even a 100Mbps link, so some can be eliminated immediately through poor networking.

Boards with gigabit Ethernet are likely to be important for your purpose, and so is fast storage it seems since you have quite a few applications listed that will require it.  That probably means you need to focus on boards that provide SATA, which eliminates another large raft of boards.  The combination of gigabit Ethernet and SATA is still a bit rare, with only Sabre-Light and Wandboard offering it among previously easily available ARM boards I think (not sure about Gumstix Pepper, but it does at least have gigabit).  You can now also add the InForce IFC6410 that you mentioned to the mix as well -- I hadn't heard of that one, but it seems well spec'd, if a little costly.  If you also add x86 then your options expand dramatically, for example with the Minnowboard, but at considerable cost.  The options are numerous.

I suspect that the best power/performance is likely to come from mini-ITX or downmarket Core i3 boards, but we haven't really been focusing on them here.

We're currently enthusing about the forthcoming A10-OLinuXino-LIME boards from Olimex which hopefully will be available by Xmas,  Although they don't have gigabit Ethernet, they do have SATA, so if I overestimated how much networking throughput you'll be needing, you might want to wait for those to appear --- at just 30 Euros, they'll be selling like hotcakes, and you could afford more than one which will give you more effective network throughput.

You have an awful lot of options!

Morgaine.

PS. Depending where you are located in the world, the Cubietruck [aka. Cubieboard3] might be an option for you as well, providing gigabit Ethernet, SATA, and dual core Cortex-A7 for less money than the InForce, and it's just become available according to the Cubie website.  The ARM price leader for that kind of spec though seem to be the various models of Wandboard.  Once it's out, Olimex's A20-SOM and its EVB baseboard is expected to provide very good competition --- the great combination of gigabit, SATA and Cortext-A7 again.

PPS. We have measurements of "SBC CPU Throughput" as well, in case that might be relevant to you.

I do all of that and more on a little Intel Atom 230 today and it's proven to be more than capable.  You're right to think that it will be more work to get things running on an Arm board (any arm board), but if you're ok with Debian then most of them have access to some variation of Debian already. Other distros can be more troublesome.

Today I'd say the only real reason to go for an Arm board is if you want to reduce power consumption. Once you've made that decision you then have to decide on what compromises in performance you're willing to make to meet your power consumption goal.

The one thing to keep in mind when looking at Arm boards is that they typically don't have lots of memory, so full desktop distros with all of the junk they drag along for the ride may be wasting what resources are available. Especially things like mysql and subversion will do better with more memory. If possible I'd suggest moving your version control to git, I find it's generally faster than svn and uses less resources and so performs better on lower end hardware.

The last thing to note is that a lot of the Arm boards want to have the OS booting from SDcard. If you're at all interested in performance, try to avoid that. SDcards are usually optimised for very different uses than general OS boot disk and can be a real performance limiter. I've finally got several embedded boards booting from SATA and the difference is amazing.

As Morgaine says, boards with gigabit ethernet & sata are few and far between. Then, depending on where in the world you are, you find it can be less than easy to source them, or that a notionally $100 board becomes $300 by the time it gets to you.  If the cost of the Arm board exceeds a cheap mini-itx Atom, then you have to start seriously examining what the reasons are for chosing one.