the intel guide is probably suggesting 12 actual cores, possibly the E5-2680 v3. so with dual xeon it would be 24 cores/48 virtual.
adobe's software doesn't need the features on the quadro's, so using the nvidia gtx desktop/gaming version can help save money.
if you need 10bit out for color correction, display out cards from mfg's like blackmagic, aja, and others can be a better option.
have you already purchased the motherboard?
hardware requirements will vary for different media types and project setups like multi-cam. codecs like h264/5 are very difficult for the cpu to process and the gpu should be handling it, but premiere doesn't currently support gpu accelerated decoding/encoding. that is what can lead to needing dual xeons as intel recommends. dual cpu's also have a large overhead, which reduces their combined processing power. another reason why intel may recommend the dual 12 core cpu's. if you are using less demanding codecs like prores or dnxhr, the cpu's wont have to be as powerful and may even be possible to use one cpu. some people transcode their footage from difficult codecs like h264/5 to prores or dnxhr as a work around instead of buying a more powerful system to handle h264/5 while editing.
from Intel's pdf: "Hardware Performance Guide: Serious 4K Editing"
It's important to note that software engineers must write specific code to take advantage of some features like multiple cores (multithreading) and virtual cores (hyper-threading). Mainstream applications like Adobe Premiere Pro and Adobe After Effects already take full advantage of these features.
if you check the testing done here: Tweakers Page - Deciding between a single CPU or dual CPU and read thru the threads here and other websites, you will find results contrary to that last sentence. adobe's software has long had problems fully multi-threading, premiere isn't as bad as some of adobe's other programs, but can still have problems.
First of all we need to know what 4K media you will be editing. Some of the more recent 4K media cannot be edited with CS5.5 or CS6. Example Sony's professional XAVC high end cameras at up to 600 Mbits/sec will not be editable unless you upgrade to CC. While the Sony consumer 4k cameras use XAVC S up to 100 Mbits/s and this is editable in CS6, I am doing it on a CS6 laptop.
Thanks for advice. I'm still not sure if I'm going to go with Adobe; there is also some very good software from Avid and Sony, and a Quadro card is designed and qualified for 24/7 use (which I may need in the future, if all goes well...). I've yet to purchase any parts, so I'll check up on Blackmagic cards.
I think you may be right in saying that the quoted figure of 12 cores is related to physical cores. I'm guessing the PDF would have stated total cores if it meant to include virtual cores.
Thanks as well for the heads-up on using dual CPUs. I had a sneaky suspicion that you wouldn't quite get double the computing power, and after reading that article you linked, I can see how a high-core E5 would be absolutely wasted on a lot of Adobe's offerings.
Cheers for info Bill. Starting off most of the work I plan to do will involve consumer grade footage, but in the future if all goes according to plan, I will be in the 'Prosumer' bracket. (Hope I'm using the correct word there...)