Really not wanting to poop on anyone's parade but an off lease Dell/HP/Lenovo workstation used from eBay will beat the pants off anything else for homelab. You can get an E3-1240 V2 with 8Gb RAM for the kingly sum of ... $200. Including motherboard, chassis and PSU.
And you're also stuck with a $200/month power bill and the full home heater....
Don't get me wrong, I have a bunch of rack pull servers and they're great for the price but I colo mine for less/server than the power bill/server would be at home and have them ona faster connection. I stick with low power options for light in-home usage
The single-socket Xeon E3 that GP mentioned is 69W TDP. The Ryzen 1700 is 65W, while the 1700x and 1800x are 95W. Why do you think the Ryzen box will be a lot less power hungry?
It doesn't matter what the TDP is. Home systems like HTPCs and home servers will run at their full power a very small amount of the time they're running. That means their maximum power usage (which is what TDP is supposed to indicate) does not matter.
Modern processors do some clever tricks to minimize using power if it is not needed, and have gotten progressively better at it. For home use cases, it's often worthwile to spend more money to get newer or otherwise more efficient PC components. This is especially true in areas where electricity costs are higher (e.g. average price per KWh can be almost twice as high in the Benelux when compared to the US).
One thing to get an indication about how good a CPU/chipset is is idle power usage of a system. It seems Ryzen is even better at this than Intel's already excellent Sky/Kaby Lake architectures [1], possibly because of the fact that Ryzen motherboards contain fewer components. On the contrary, the Ivy Bridge architecture of the chip mentioned by the parent cannot be considered competitive from a power consumption perspective, despite still being a great performer.
The Ryzen 1700 has 8/16 and much better performance compared to the mentioned Xeon E3. I think the Ryzen 5's would be the ones to look out for (still more cores and much less price), hope they push the power consumption even lower.
"beat the pants"? Compared to Ryzen, E3-1240 V2 has: half the cores, half the L3 cache, half the memory throughput of Ryzen, no AVX2, etc. Plus average price is more like $300-350 http://www.ebay.com/itm/Dell-PowerEdge-R210-II-1U-Rackmount-... And it's still comparing apples to oranges favoring Intel. Wait a few months and compare used Ryzen gear to that old Intel gear...
Depends on your needs, dual socket xeon servers can be had with huge amounts of ram if you shop around. E.g. I got an IBM 3650 m2 with 2x L5640 and 128gb of ecc ram for $200. For my needs (heavy data processing on a budget) its been awesome.