Talk about missing the mark completely. This is a workstation for professionals not some kind of gaming machine for kids to be playing on at home... You are comparing apples to oranges when you are starting to mix consumer grade hardware with workstation / server grade ones. It's like telling Amazon to start running their servers 24 / 7 on non-server hardware, or telling them to start using Belkin routers instead of Cisco Enterprise ones because they are cheaper and might be comparable in a performance only situation.
These are workstations tended for studios and professions, its something that upscale studios like Disney Pixar, WETA Digital and the like use to render their animations on, something that larger television networks are using for editing their content before its being broadcast.
For situations like this its often more expensive to have a few hours of unnecessary downtime due to software and hardware issues than its to pay the premium for workstation grade hardware. That's why we have workstation grade hardware in the first place, they are cherry picked by the manufacture, tested and verified to handle 24 / 7 usage without hiccups and large scale companies are willing to pay the price premium for this.
Starting to compare with consumer grade hardware is just silly, and you also include ECC registered memory even though the CPU you have chosen does not feature a ECC compatible memory controller.. And no company in their right mind would ever do any kind of serious workload on a system running non-ecc memory to begin with. You SSD isn't even running of SLC flash so it's basically useless for anything write heavy related workloads as those kinds of consumer SSD's are not design for this kind of workflow and would normally fail within the first year depending on how big the workload would end up being.
Your motherboard does not feature any kind of workstation grade chipset, doesn't come with any Thunderbolt ports and features dreadful Marvell chipset for the additional SATA ports which is as far from workstation grade as you'd get with this kind of thing.
You also behave like the R9 280x is anywhere near the computing and opencl peformance of a D700 which it's not by any stretch of the imagination. It's like saying a GeForce GT 620 is just as capable as a GTX 780 Ti to a gamer. You also include a display which is not featuring good enough calibration for the kind of work pro workstation like the Mac Pro is supposed to be handling.
Good luck next time is all I can say to this rubbish.
You so have no clue what you are talking about so I will have a field trip ripping apart your comment.
First of all you have no clue what is the difference between workstation and server. Server is the one that requires to run 24/7 while workstation requires performance first then durability. Since base Mac Pro is you typical "prosumer" PC and not a heavy duty workstation by any means that's exactly how I've speced a comparable PC.
i7 is Ivey Bridge E on LGA 2011 socket, reason why it supports ECC memory. As a matter of fact 4820K owns 1620 v2 when it comes to speed, single core or all four cores.
840 EVO uses TLC and SLC for secondary caching and in RAID0 it will give you comparable speed to PCIe SSD. I don't know what kind of workload you are talking about but I assume you are talking about video since that is that is the only workload that is stressful enough to kill the disks. Well guess what? With 250GB you will not be able to do any kind of heavy duty workflow there is just no room for such thing.
Thunderbolt? You don't need a Thunderbolt since you have actual SATAs. And nobody is forcing you to use Marvell if you don't need many drives inside your housing. No reason to spec Super Micro motherboard for prosumer workstation.
R9 280x will outperform D300 in single or dual mode no problem in OpenCL computations. Actually R9 280x outperforms FirePro W8000 by a small margin in OpenCL. Your only limitation might be the actual software that recognizes only FirePro or Quadro cards like SolidWorks, but there are hacks to get around it. And don't for a second believe that D300/D500/D700 are carbon copies of FirePro W series. They are most likely a customized 79** series silicon as both D700 and R9 280x are based of 7970.
And to conclude that you do not work in professional or studio environment, like you say, I will just let you google Eizo CG323W since you have no clue what it is.
This was way too easy.
BTW somebody mentioned ASUS 250GB PCIe SSD. It sounds good on paper but in real world usage its is slower than SATA 6 840 EVO unfortunately. Its not a good buy, just avoid it. If you crave for speed you can go with OCZ R4 but if you want the cream of the crop I think Micron P320h with some stupid 700K IOPs