To be honest, for the best bang for your buck it might be worth to get some of the parts used, especially when you compare to used hardware anyway. I am specifically thinking about the GPU for example (from someone that wants to upgrade).
What resolution does he need? (And what color accuracy) The screen may be the hardest part here.
I agree with @psycho_666 that the 8700 would be better for Adobe Premier and Aftereffects but from the overall value I think 2700X (or 2700 overclocked) makes sense when you include cinema4d (what @flazza said) It depends on what software he uses the most. Also the 2700X will be a lot faster than what is in an old iMac anyway.
I would shave some money off by using a sata ssd, there won’t be a noticable difference most of the time.
Regarding Raid: I would rather use the second hard drive as a backup drive or ideally use a NAS as a backup location (if he has one) and cut the second hard drive.
Which features does he want in the motherboard? I thing you can go a bit cheaper than that.
What iMac are we comparing against?
Edit: It seems like most functions that use open-cl also can utilize cuda, so the elephant in the room is whether H.264 encoding is worth it going with intel or not. If H.264 encoding is not that important I would say go with the 2700(x).
This is the reason I would recommend backup over RAID. You can have incremental backups like “TimeMachine” on mac OS. Set it up once and never look at it again. In my expereince user error (i.e. accidentally overwriting a file or needing that one folder back that you thought you don’t need any more) is much more common than a disk dying and you are protected from that too with backups. Also there are those people that don’t replace a dead disk in a RAID.
now I am desparately trying to squeze in a good 2560x1440 panel lol, rip me
For me it is important to know the importance of the screen specs. Some people buy the iMacs only for the screen.
Also, the more I look, the more I am inclined towards the 2700X. I think that’s the better choice (except when you get something used for cheaper, lots of people are upgrading around now).
Does he have thunderbolt peripherals or need thunderbolt? (I want to save you the “but obviously I need thunderbolt, why doesn’t it have thunderbolt” discussion.)
If you’re planning to also render for a couple of hours or more, I would suggest you stay away from iMacs. The thermals on those leave a lot to be desired for sustained loads and if you factor in 5years age and realize its an all in one, it could be a risky purchase. If you must have Mac OS, you can go a Mac mini sized hackintosh or Mac Pro for best cooling and performance. For that budget you could go 7th gen instead too to have more tried and tested build reviews to choose from.
Otherwise, I would definitely go the 2700x route with a midrange maxwell gpu.
In the distant past I have had very bad luck with Seagate drives. Currently I’m using HGST drives with no failures. And 1 Toshiba failure this year.
Keep in mind two new drives in raid 1 are wearing evenly and do stand a chance of failing at the same time.
I have used raid 1 in the past but now I’d probably use 1 drive as a storage pool and the second for weekly backups. That would probably stand a better chance of data retention. Raid 1 is usually good for keeping the system alive in 24/7 environments.
The CPU is a tough choice, sure Intel performs better in Adobe but the CPU prices are so far apart it seems silly to not save money and get the R7 2700, but that depends on how far behind it is from the i7 8700K in Adobe software. Even then you could put the rest of that money towards a better GPU. Why buy an i7 8700K and a GTX 1050 Ti when you can get an R7 2700 and a GTX 1060?
As for the iGPU acceleration, I am lost on that, does this really help in any meaningful way when you already got a GTX 1050 Ti planned there? The GTX 1050 Ti is more than twice as powerful as Vega 8 and Intel HD 620 is about equal to Vega 3. Again, I don’t know how this is utilized, maybe the software has some clever tricks I don’t know about that help.
Going back to the GPU, wouldn’t a GTX 1060 be a better buy for this? (Note that if you need CUDA, I am not so sure if the RX 570 and 580 are such good options but they might be better than a freaking GTX 1050 Ti). If the budget is too constraint and you need CUDA, then I suppose a GTX 1050 Ti works until you feel like upgrading.
Edit: Oh yes, forgot to mention, get 16 GB of RAM for now, RAM prices suck because RAM manufacturers decided to suck.
Not gonna happen. That is easily 400,- bucks alone. Get 16GB of good memory now, get more later if necessary. Gskill TridentZ 3200 CL14 is super solid and (on my X470 Taichi Ultimate) runs at full speed with 32GB in four sticks.
For the monitor: Dell U2715H.
970EVO is great but don’t make the same mistake I did, get the 500GB version. It is less money / GB and the bigger drive is also quite a bit faster.
Personally I would go with the NH-U14S instead of the Cryorig but that is purely because I’m fangirling for their stuff. In terms of mounting mechanism and especially the performance to noise ratio Noctua is still king. It is a couple bucks more though.