Thank you for all the feedback and ideas.
oh yeah sure, for electricity cost you need to decide, is the server idle more or under load more?
As mentioned before, like most of homeservers, mainly idle.
But then the Xeon will have more intangible advantages like IPMI (probably), lots of PCIE lanes, more and cheaper memory support.
These are the advantages I also see.
I actually removed one CPU from my dual CPU board just to save on electricity costs.
Here I am clear what I want. A single CPU board providing me the number of cores by a single CPU. I prefer 1x E5 V4 over 2x E5 V3.
I think the first thing you should decide on is whether you need more than 16 lanes of PCI-e or 256GB of RAM. If you do, Xeon V3/V4 is basically a no brainer, since your only other reasonable option would be Skylake-SP, a much more expensive platform with fairly marginal improvements over Broadwell (16 core Skylake is probably 20% faster than 16 core Broadwell, most of which comes from high clocks).
The key of the question is in "need". To be honest, nothing of this I really need. I am talking about "want to have" and I am balancing what I get against costs (invest + operation costs). For me it is fun to have an oversized IT system at home and to do things in a complicate way. It is satisfaction to me when my neighbor is wondering why my WiFi reaches to the garden and my family is wondering that I can share data and blogs without cloud.
My current old system is running and does its job. What grinds my gears since years is its RAM limit of 32 GB. Now I will move forward and want to figure out how far.
So if you don't need every last percent in single thread performance, I still think a 2011-3 system makes a great home/soho server on a tight budget.
Yes, this was the reason behind why I got the idea of a 2011-3 system. More cores than my current 4, but no high single thread performance.
Actual power draw completely depends on the actual CPU(s) used and the workloads you put on the system anyways, and the power efficiency isn't increasing as rapidly with those newer generations as it did ~10-15 years ago.
This is what I had expected and the core of my original question. I assumed improvements for newer generations but no revolution.
If you don't need that much compute power, you might as well look at some of the Xeon-D15xx options (or the newer D21xx if on a bigger budget), which even have dual 10GBit on-chip.
I checked out the D21xx. But all integrated platforms are quite expensive and not much to find on used market.
10 GBit SPF+ integrated would be fine but hard to get. So one PCie slot for my existing SPF+ card.
Build-in SAS also would be fine as on my current E3 system because my storage HDD drives are SAS. Or one more PCIe slot for a SAS controller.
As GPU are mentioned: I forgot that this server also has a Quadro P400 for transcoding (I run emby in a jail on it). This card also adds ~20W at idle...
No plan for GPU by this time. But nobody knows what idea I will get in the future. Spare PCIe slots I will keep in my plan.