It is inevitable that sooner or later you primary Lightroom editing device will fail, and you will be rushing to replace it with 48 hours of the event. There will be little time to examine the options, which have likely changed substantially since you last bought your device. So if this was to happen in the later part of 2018 what options should you consider. Most photographers, in a perfect world, like to be able to do some heavy duty processing at home but some processing in the field especially if you are spending a lot of money travelling somewhere and you want to make sure you got the shot you want. I would also want to assume that you would want to use Lightroom and its integration with Photoshop to edit. So two approaches emerge in my mind use an iMac in your home system and an iPad in the field. A second option might be to use a laptop in the field that can be docked to a larger screen and other devices when you are at home.

Approach One

Approach Two

Basic Requirments

A full frame digital camera like the Sony A7RIII creates an 83MB file and the medium format GFX50s creates a 121MB a photographer’s computer should be able to handle these file sizes with ease. It should also be able to create a large photoshop file from the image while both programs are open. If you are a medium format shooter with Phasefour 325MB file size one would hope the computer could handle this as well.
So what is the minimum configuration that will allow you to use these programs? Well, there is nothing like real-world experience. Recently I was processing in the field on a MacBook with 8GB of RAM and at the time had to merge files to create some panoramas, the largest file I processes was 153mb. In the field, Lightroom handles all this process with some delay with larger panorama merges.
So taking the largest panorama file at 153MB had Lightroom edit this file in Photoshop, the file was panoramic knit of 13 shots, moving this into photoshop took 2 minutes but resulted in a TIFF file of 99mb. But if I doubled the size of the file it did not seem to be able to return the file to Lightroom. The MacBook is a 1.2 GHz Intel Core M with 8 gigs of RAM. So clearly you can create large files but not manipulate them in Photoshop while Lightroom is still open. So clearly the one needs at least more ran to be able to move between programs with a large file.
A minimum of 16GB is required, and 32GB is ideal with regard to future proofing. Keep in mind 16GB is currently the most RAM available for the MacBook and 13″ MacBook Pro models. To speed up process it would be helpful if the device had SSD memory, here 1TB would be ideal but with USB-C speeds through thunderbolt drives one could make do with 1/2TB of SSD. In terms of the processor a minimum of four core and ideally 6 core. Also having separate RAM on the video card would speed things up as well if possible.
Having said all that if you are using only Adobe Lightroom CC, then these specifications would change significantly, and one might even be able to process everything on an iPad Pro.

A Cost Comparison

MacBook Pro

MacBook

Pros and Cons of MacBook Pro and Large Screen

References