Odd and interesting situation. (sorry for any interruption not allowing me to sub a new thread)
Just purchased a base model 6-core. all for nle. avid and fcpx. Bought in a hurry before year end, just broke the seal this week, due to connectivity ext I had to purchase another keyboard/ track pad to pair to each machine accordingly when transferring screens in target disc mode. this is something apple had a very hard time answering for me prior to purchase.
I'm now unsure if I need to feel some buyers remorse based on the numerous positive reviews on the new reiMac.

cpu/ performance/ and the 5k display loaded up for a tad less than a macpro seems unbalanced.
my current iMac is basic late 13' 3.2 refurb. had a ridiculous amount of problems using fcpx last year while rendering. would crash 4-8 times a session so I wasn't sure how much I would gain with a loaded up reIMac
also will be shooting more 4k. and noticed the rendering from 4k to 1080 crushed the macpro vs the iMac. not sure how or if I would do that very often but some of the processing times on adobe based software also was alarming. wondering what the current pros in the industry might recommend. meanwhile I hate to use the late iMac as display simply due to the obvious reasons but I wouldn't get enough out of selling it to even buy a worthwhile 4k display. (not sure if this is a bad thing?) my grind is deciding if I should cash in both macs and settle on a 5k and heat up the room on ocasion or was my initial investment the right move
How often do you render, on occasion or is the iMac5k going to be on fire at least once a day?
My story, I went from Mac Pro to custom built PC, to a iMac5k. Lost a lot of money in the process, waiting for the 5k to come in right now. Got one last week but counted over 10 dead pixels (you can't see them unless they are clustered like mine were). In the time I had it, I got to play with it some more. I realized how important the screen is for me. But keep in mind, I'm getting it solely for the screen. I think if the Mac Pro supported 5k and there were screens out there, I'd go Mac Pro all in and this thread would not exist. It's whisper quiet no matter what you throw at it, and if dual monitors is a must, it's always nice when they actually match. But my issue, is I need at least 1 good screen to stare at 14 hours a day, whether text, code, graphics, etc. I don't render / convert but my VMs do sometimes spike 100% cpu.
Until the technology for external 5k screens comes around or at least a better quality TB display, I'll stick with the iMac5k. From what I hear, we are a long way off 5k and a good TB display is not in the works and we may never see one. I do suspect, it's possible, that one will be released with the new MBA. It's my prediction because the new MBA will not have a TB port (based on rumors anyway), and I can't imagine Apple will leave dock/external monitor not around for the MBA.
So for you, if you have good monitors, the Mac Pro is a beautiful machine. I did a bunch of tests with the Mac Pro vs 4ghz iMac and outside of benchmarks for single-core there was not much of a difference. Also keep in mind, while it may be faster on **some** tasks, it will come at a cost of risk of fire (joking of course, but you know what I mean). To get the speeds that make it faster than the Mac Pro, it's giving everything it has. But the Mac Pro keeping up with the iMac barely moves the fan if at all. And there is no doubt that the mac pro can keep pushing that speed for days if not weeks without a hiccup.
But again, that's all dependent on what you use it and how important the screen is for you and if you render, etc, and how long you do it for.
Going down every single path possible (including PC, which I actually kind of liked), I'm sticking to iMac ONLY because I can't find any good screens for the mac pro. And I want apple screens. I want brightness control, and no weird wake issues like all the dell 4k screens have. And if Apple does release good monitors (even if they are the non-retina iMac screens) I will sell iMac and get Mac Pro.
All being said, I did feel better having $5k back in my bank account and only spending $3800 on the iMac. Not too big of a diff, but big enough.
Are you thinking of the iMac for power or solely for the screen? I agree with Tim Cook, it's a screen with a free computer inside. Happens to be that computer is nice, but the screen is what the iMac is.
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For finding a monitor that will work for the next 6-12 months, these MacWorld articles look like a good place to start. After all, they're reviewing them for use with Macs!:
http://www.macworld.com/article/259...ys-wide-color-gamut-ideal-for-production.html
http://www.macworld.com/article/215...iracles-from-this-inexpensive-4k-display.html
Also, one reviewer on Newegg (for the Samsung 4K monitor) said he's had problems unless he uses only Apple cables when connecting to a Mac. I don't know if there's anything to it, but it's certainly worth the small investment considering all you've gone through.
I tried a 27" 4k screen and the scaling is awful at that size. It's either 1920x1080 with text being too big, or you do smaller resolutions with major scaling issues. I think Apple is on to something when they did the 5k. Not about pixels, they just double horiz/vert resolutions. The 4k 24"'s are better, but there are no good ones out there yet.