Considering the usage and the budget, I'd be tempted to go for an IPS monitor with the highest resolution possible within budget. I would drop the idea of SLI/Crossfire as well, it can get noisy and that can be annoying while you are working. Not to mention the high power consumption and possible heat and compatibility issues.
That keeps pretty much the same performance, you just lose out on SLI/Crossfire (which I don't think you need to be honest) and it gives you a fantastic monitor so you can really see the benefit of a good gaming PC by playing games at ultra high resolutions. Those monitors are perfect for the CAD work too.
^Yes, it's perfect for the CAD work, but it's not so good for gaming. IPS monitors have imput lag that comes from the lower refresh rates - I'd for for a standard TN panel. Perhaps a 120hz one. (Gaming was his first priority.)
The refresh rate is 60Hz just like most monitors. That's fine.
The response time is a bit higher but that is something that most people won't notice, anything under 12ms is usually OK for most people. It is for me at least, I have played games on 6-8ms monitors and never noticed ghosting and I don't know anyone else that has noticed it. I think only very serious gamers playing mostly FPS games would even notice.
One thing you would definitely notice though, is the jump up to 27'' and 2560x1440 on an IPS panel.
Consider getting a TV 32" or bigger, instead of a monitor.
Just make sure to get a good one. Get a nice sofa and a wireless mouse and maybe keyboard too. If you have the room for them both, and you get a big enough screen and comfortable enough sofa- you will never go back. Its amazing how advanced and cheap new TVs are.
Regular desktop monitor only makes sense if getting higher than 1920 pixel version. In most cases, you can get 2x good 42" 1920 monitors for the price of a single denser pixel monitor.
If you're worried about color quality and reproduction... don't be. To see what I mean just browse a TV store and ask them to playback some color tests. Most if not all TVs have outstanding color reproduction. Put the TV through the same tests you'd put a monitor, and you may be surprised by the results.
I switched to hanspree 42" model about a year ago and it took me a month to stop using my color calibrated 24" benq. I almost never use the monitor now days.
I'm not sure if there was something in particular you were after with that motherboard, but I switched it for one that should still be good quality and doesn't really drop any functionality. (You lose 2 of the USB 3.0 ports, but still have the potential for Crossfire/SLI and 4 SATA 6.0 ports.)
I switched out your RAM for a good quality 2x8GB configuration, which saves you money and leaves a couple slots open in case you ever need to upgrade.
Also switched to a Caviar Blue HDD, which saves you ~$20, but drops the Warranty from 5 years to two. My understanding is that you won't see any major performance increases from switching from Blue to Black, but I wouldn't knock you for going that way to get the better warranty.
Next I upgraded the SSD to a top notch 240GB drive. I think you will really be happier with a 240 GB system drive over the 128 GB you had picked. Installing 64-bit Windows, games and CAD programs can really chew up that space quickly. I absolutely recommend keeping this upgrade.
I also switched out your GPU for a good quality Radeon 7950. The XFX DoubleD cards run quietly and come with a lifetime warranty. Plus you save a little money here and shouldn't see any major performance decreases.
I kept your cases as-is because I feel that is a personal preference thing. I hate skimping on a PSU because it can kill your whole build, and I think you have chosen a great one here. This is the biggest issue I would take with the recommendation another poster made of grabbing the 550W Antec PSU (which actually only puts out 444W split between 3 separate +12V rails). 750W 80Plus Gold with a single 12V rail and fully modular will be something that should not cause you any problems.
I think that pretty much takes care of it. In a nutshell I tried to swap out some of your parts for what I felt would be better options for you while maintaining or improving the quality without increasing the price. If you have any questions (or want further detail on why I made some of the changes I made) then feel free to ask.
I added the monitor anyway I know you said you didn't need one. I dislike the Dell recommendation I know there customer service isn't very good. With the ASUS monitors like the PA/PB series you get ARR service which basically means that when you RMA your monitor they pay for it and at the same time as you send it they will send you one back. You won't get that from Dell or really anyone for that matter. And I disagree with the input lag 5-6ms response time is more then adequate for gaming 2-3 ms is a lie in most cases doesn't exist.
I also went against the flow the EVO is really really mainstream at this point. Noctua is a very strong brand there higher end cooler the NH-D14 is a boss cooler and up there in the air coolers.
I went with the HAF 912 because it has ample room for a larger graphics card and comes with the components of a more expensive case while retaining the look of something more expensive as well.
Windows Professional is nice however that may be something you may want to change to home premium depending on if you intend on ever going beyond 16 gig's home premium's 64 bit limit is 16 gigs where as professional is something like 192 gigabytes.
I also think its better to go with the nvidia cards with CAD because you get access to CUDA.
Fair enough if you want to use your current monitor, the build I suggested minus the expensive monitor is still good value though. Pretty similar performance to your original build for a lot less cash.
I mean all in all with his build there isn't really anything wrong with it. He has different brands up there but ripjaw ram isn't bad the m4 isn't a bad SSD there may be a little faster in that range but still not bad. The 670 isn't a bad card for a balance of cad and gaming. All you are doing by moving down to the 7950 is saving $150 or so dollars but with your budget around $2,000.00 I don't see an issue going with the superior card for gaming and for cad.