A few things to note. 4k at 400mbs, that will work on an SD card, your dealing with a great amount of compression. To work around it as other's suggested, in fcpx you can turn off background rendering and set to proxy for your edit. Or option 2 prior to editing, transcode all of your footage to QT prores which will tax your machine less. When selecting a computer go to a specialist and have the main drive(s) the fasted blade type ssds. On location I have two customized 2015 mbpros that are faster than the 2016/2017 once the drives are swapped and some other tricks the company does.
In DiVinci Resolve 12.5 which is a very heavy program I can burn through RED 4.5k ws raws like crazy on this little powerbooks and I keep all the raws on ssd's, the render files on a separate ssd. Even my 1dxII which uses an older codec, (motion jpeg) and shoots from 500 to 800 mbs setting the viewing in proxy, 1/2 resolution, it runs through those masters fast, depending on the amount of filtration I use.
So bottom line, it's not just the computer, it's also the type of drives your running and the original file codec.
Hope this helps.
IMO
BC
The thing is that motion jpeg, in spite of being stone age, does not demand heavy calculations.
So the files are bigger than more optimised codecs but then they are easier to deal with
For the softwares.
I found with Red that Mistika handles well 4ish kays on limited computers cause it's a software designed for being forgiving (like Nuke) in that aspect, however 6, 8k is another planet and it bloody slows down a lot.
What I discovered with Red, is that Lightworks (I know nobody uses it anymore except Scorcese and me...
Well, the King's speach was cutted with it) just handles R3Ds of all reso through proxies that it creates on the fly very fast.
The advantage of this appraoch is that you switch full rez / proxies any time with a simple switcher. There are also no (re)linking possible issues.
I never liked the prores proxies because there are more files to link.
In lw I use R3Ds (and can affect the rmd) dorectly and give the software the task to create its own proxies that it only uses
When editing but there is only one file: the Red's raw.
I can't work on real time in Lightworks (nor Mistika nor Resolve) with Red decode at 6 or 8k. I'd need way more power and it's too costly and I don't have the rockets. With proxies it's a breeze.
Don't compmetly agree with this:
https://www.redsharknews.com/post/item/5424-lightworks-is-so-efficient-you-can-edit-8k-on-a-laptopNow, your customized computers look interesting.