Just remember that to get this NEC display will cost more than your entire iMac,
MSRP is $3,249. No exaggeration to say that a Mac Pro with NEC display that performs as well as the i7 5k iMac will cost a decent amount over
TWICE as much money.
Personally, I've worked in print for almost two decades and I stopped using the high-end calibrated monitors a while ago. I found they still required me to do my own in-head conversion to visualize how it would actually print (backlit RGB can never do more than approximate a printed CMYK image), and that I could do the same conversion work from a less-than-perfect monitor after not too many jobs done on it becoming familiar with how the screen image translates. Well, that and really getting to know my Pantone Process Color books

And if it's a job big and important enough to need to be absolutely perfect, and something crazy happens where the proof doesn't actually look like I thought it would, then I pay the small fee to do an adjustment and re-submit the files (has happened two times in last five years). That extra $4,000 or so you are spending to get the NEC display would pay for a freaking
ton of proper proof prints, which would be more accurate than any display could ever be. Just saying.
And, also, if you do web design work or work headed for the web, a non-calibrated display will give you a far better idea of what your images will look like for the average bear, who just turns it on out of the box with the defaults and never thinks about it again.
On the other hand if your work on this machine is generating $100k in profits every year, then, yeah, spend that money! It's all about cost/benefit and needs of course. Your decision to wait and spend twice as much money is totally valid, and I understand your motivationI'm more offering my perspective just to provide a different opinion based on my experience.