For a MacBook, LG's 34" is hard to beat.

At around $800, it's cheaper than Apple's 27" displays, and is bigger and has more pixels to boot.

It's the only non-Apple display I'm aware of with Thunderbolt, which means you only need one cable for video/audio/usb. Standalone Thunderbolt docks exist but are a couple hundred dollars.

The only options for bigger are 4k displays, and I know I can't run 4k at 60hz from my 13" MBP, not sure about the 15.

http://www.amazon.com/LG-Electronics-34UM95-34-Inch-LED-Lit/dp/B00JR6GCZA

Hopefully I'm not late for the party, but here's my input.

• As Anirishguy13 suggested - go for the NVidia.
• Go for a monitor that will display true colors for color correction. HP Dreamcolor is generally good for the price, as most are super expensive. I know of on-site professional colorists who use dream colors. More of this was actually covered in a recent thread. Moreover, if I can recommend something, if you're looking to dual monitor, and I can see you are, I would go for the LG 34UM95. I've been wanting to buy one and actually saw one in person yesterday, and I think this will be one of my next purchases. It eliminates the annoying bezel in the middle of the monitor.
• Personally, I use my ATH-M50 as my headphones. I almost exclusively use those headphones for weddings. I'm not a big fan of speakers. I'll catch flack for this, but the reason is, for me, I get to hear every single detail with my headphones. Once everything is mixed, I'll play it back on my speakers to make sure volume is good.
• I'm a supporter of overkill. I made sure to go for 64GB RAM.
• I personally like smaller keyboards, something like apples - something really compact. Also, go with something that isn't mechanical. They're too noisy in my opinion.
• If you plan on adding another graphics card down the road, or just beefing it up, I'd go for a 1000W powersupply (again, I'm a believer in overkill)

Also I sort of get the feeling you built this to accommodate gaming?

PS: Good choice on the case. In the three years I've had my editing PC I have yet to hear any noise. I've literally kept it on over night on several occasions to export and I don't hear a peep. Make sure you have an ample amount of fans.