But srsly, lots of CAD (often includes rendering), office work, sometimes gaming, running game servers, a lot of virtualisation and I got a bad habit of doing all those things at the same time
I know I'm going to get flamed for this... but here goes.
I don't like the idea of buying older Xeons to put on a $400+ motherboard just because Wendell did it.
I'd say just buy a whole complete server. You money goes way further, and you can spend the savings on more RAM
Or you can do what I did and buy engineering sample CPUs. If I had to do it over again I'd buy the cheapest 12 core CPUs I could find and save $1500. Here's my system (cuz I like to show off): https://pcpartpicker.com/b/b8LD4D
(and I´d be be basically using server components outside a server enclosure with a non-redundant power supply and different cooling, soo it´s not that different from the real deal.)
The 1U and 2U rack mount servers are pretty fucking loud. I totally agree. However the towers, which are like 4u or 5u in size (and can usually be converted to rack mounting) aren't too bad. You can even unscrew the internal heat sinks and put in some coolermaster 212 or whatever flavor you like.
My system is dead quiet tho.. and that was one of the requirements I had.
There are lots of ebay postings for ES CPUs and a lot of them list which boards are supported. I took a chance and everything worked for me. I was a little lucky because my mobo shipped direct from Supermicro with the latest BIOS installed (which is what was needed). That being said, I'm hesitant to upgrade my bios without confirming that the CPUs will still be supported. The good thing about my board, is that it is a year old and all the old issues have probably been ironed out.
The 3770K mentioned in your profile is still your system? So, trading single core performance for a massive number of cores. Can't see anything wrong with that. ;)
depending on your workload, having more than 2 cpus can actually hinder work, there was an article about it but I can't seem to find it. having to do with things getting more complex and programs having issues actually using all the available cores.
Then there is the whole thing about compatibility, remember to check your PSU actually has the cabling required by the motherboard and that the motherboard in question actually can be mounted into a normal case.
Heat is another issue especially if you want to have 4 cpus, as a single xeon will output X ammount of heat at idle and having 4 of them will surprising everyone, quadruple the heat output. when running a render or calculation job, 2 x xeons can draw a nice 300W of power that gets turned into heat and with 4 your get 600w meaning your computer doubles as a hair dryer.