Right off the bat, option C is out. WCG only works on regular hardware, so you are looking for normal parts.

Next, there's another thing to note: power consumption. Don't forget, these machines have to be sustained, and multiple 24/7 PCs have a hefty cost on every month's power bill.

But there's even more: would these be dedicated crunchers, or would these PCs be used for something else? Where are you located? How much can you spend? These are all important questions that can aid you into fine tuning your setups for maximum efficiency.

Uh... last time I checked, a 4790k was a gaming CPU.

And workstations are NOT a good idea - provided OP can build the PCs on it's own, then we can do much better by using custom parts. For example, cheap RAM (WCG just doesn't care), lack of HDs in favor of a single SSD to power all the systems via Ethernet boot, used cases (or even no case at all!), TFX Psus... you name it. Workstations also tend to have restrictions on the BIOS / Software they come with, and troubleshooting such machines is just A PAIN.

It would be good to have an idea of the budget range.

Having built dedicated BOINC machines myself, with charity funding, i would consider these points first

1. Hardware
The hardware largely depends on your budget, either way i would consider these factors
-Reliability (very important, highly recommended to get a motherboard with a heatsink on the VRM(voltage regulator module) )
-Efficiency (look at the WCG forums for help)
-Cooling (the cpu, vrm and north bridge will get hot. get a system fan to cool them)
-GPU (my build relies on the onboard graphics as no GPU was installed)

2. Software
-Ubuntu server (free, BOINC runs fine on it, requires you to learn ubuntu server, never have to use a GPU, ssh into it from anywhere)
-Windows (not free, assuming you already know how to work it, problematic without a gpu)

3. Location
Being secure and confident in the location that the BOINC machines will run is necessary.
Factors you want to account for include
-Accessibility
-Humidity
-Ventilation (preferable but not required)
-Temperature

My build used these components and it has been running for days perfectly
Mobo: Gigabyte 78LMT
CPU: AMD FX8350
PSU: Coolermaster Elite Power 460W
CPU Fan: Cooler Master Blizzard T2
RAM: ADATA Premier Series DDR3 1333Mhz 4 GB

Hi, CharityHost,

You might want to check on ES (engineering sample) Xeons on eBay. You can find them there for a fraction of the price of a retail unit, so that method can be an awesome price-to-performance ratio. Just keep in mind that with those, you'll either need to run your OS headless or get some sort of GPU, even if it's just enough to run a display. I bought an E5-2695 v3 (14C/28T, 2.5GHz turbo) for $550 and it works great.