I run a couple of VMs and two versions of Citrix to connect to external past DMZ Win7 VDI desktops plus local Visio, very heavy Excel, Illustrator (mainly, but some InDesign and Fireworks) plus multiple browsers with perhaps up to 40+ tabs open. Then we have SQL local and remote and perhaps a dozen email accounts open at the same time, permanently.
Illustrator prior to 2014 doesn't appear to support GPU acceleration, acceleration 2014 only supports nVidia and Illustrator 2015 supports all graphics cards. Performance variation between graphics cards is a difficult subject to find information about. The only thing I could find was on the nVidia website and they're obviously keen for people to spend as much as possible:
Adobe Illustrator CC and Quadro GPUs provide huge boost for High-Resolution Creative Design
Hardware wide the three cards there are equivalent to a GTX 970, GTX 750ti and half a GTX 750ti but the quadro range does use different drivers which can sometimes affect performance.
Given that's the lower half of the range and they're fairly close together I would suspect it doesn't greatly benefit from faster cards and something at the R7 360 or GTX 750ti level would be appropriate.
HDDs are WD Black in situ with RAID on WD Red via networked NAS.
But which size are they? Western Digital makes both ranges in 2.5" and 3.5" sizes but not every case will have four 2.5" or four 3.5" drive bays. 3.5" is more common on desktops, but there are a lot of 2.5" drives around these days too.
Not sure why the i7 versus Xeon would be a choice. I tentatively chose the 5820 due to breadth of power and hoped for longevity. Happy to review if needs be.
The Xeon range gets ECC memory support. I don't have much experience in that area but I gather it's for things like scientific models of CAD work where a minor error could cause a manufacturered part to fail or a scientific result to be in error.
It's also where Intel puts their big workhorse processors, the desktop 'enthusiast' range that you're looking at uses the smallest Xeon chip with just 8 cores with some features like ECC support so they don't clash with the main market.
The 5820k is good value for money.
I look at Skylake and DDR4 as being the best current option for a system which will hopefully last 5 years with minimal upgrades. I am not really going to push overclocking on day one.
Skylake is the 6000 model number processors. The 5820k is a couple of generations older being Haswell-E. The large Broadwell and Skylake chips aren't out yet.
I also see the Samsung and Sandisk options you note. I am heading for the Samsung at present.
It might be worth considering a drive like the Intel 750. Normally they're a waste of money because they work best when lots of things are accessing the disk simultaneously and it's rare that more than about two happen at once. With multiple SQL going on at once you may benefit though.
If you don't think that would be worth it I'd still be inclined to go for a higher speed drive focused on a low queue depth like an SM951.
Motherboards are where I have the greatest worry as I have no idea except to read and follow unknown advice.
Buy on features. Reliability is not going to be a concern when the cheapest cost £150 so just go for whatever ports, expansion slots and capabilities you need.
As for cases, nothing stupidly childish or garish but a simply box is fine. Quiet and reliable are the main requirements.
Reliable is an unusual requirement for a case because there's not much on them to fail. Will it be moved around a lot, or have the front ports used an unusually large amount or any other uncommon behavior that might cause issues?
