Buildin New PC for Photoshop/ Lightroom Kaby Lake vs Coffee Lake?

With Photoshop's UI scaling issues it nice to have Low and High resolution displays on your system and not use Adobe 2x UI... Screen captures

You do not state what your budget is.  Photoshop does not require the best computer available out there. I like Coffee Cake and like to have money to buy Coffee, Cake and wine. So I like to buy as few computers as possible and not spend top dollar for the systems that I buy.  I made a rule for myself that I follow and works well for me.  Buy last years top of the line machines that currently sell for between $1,500 and $2,500 and use your old good hardware with it. Like Displays, Wacom tablets, mice and External drives.   There is also nothing wrong with buying refurbished equipment either.   I have been particularly happy buying refurbished Dell works stations from Dell Outlet they come with 3 Years of Dell Service.  You need to monitor the Dell web site often to find a machine you may want for they sell quickly so you need to know what you want and when that type of configuration become available pounce on it before someone else does. Last week I bought one for my son for  $1,565 here is what he now has. It would be a great machine for Photoshop if he used Photoshop.

Dell Outlet Precision T5810

Processor: Intel Xeon E5-2630 v4 Processor (10 Core, 2.2GHz, 25M Cache, 85W)

32 GB DDR4 RDIMM ECC 2400MHz (4x8GB) Module,Dual In-Line Memory,Registered Dimm

256GB 2.5Inch SATA Class 20 Solid State Drive,S3,7MM,PM871

NVIDIA Quadro M2000 4GB (4 DP) (1 DP to SL-DVI adapter)

8X DVD ROM Drive Digital Video Disk Drive,8X,12.7T,Hitachi Lg Data Storage,BLN

Dell KB212-B USB Keyboard,104,United States

Optical 2-Button Mouse Black,Logitech,DI

Internal Speaker

Hard Drive Bracket

Precision T5810 425W TPM Chassis

Windows 10 Pro

Windows 64 Bit

Wave Systems Software

3 Year Hardware Service with Onsite/In-Home Service After Remote Diagnosis

The Dell Workstation I purchased in 2013 for $2000 is still serving me well but is less powerful. Handle Photpshop well. I do not use Lightroom.

Dell Outlet Precision Fixed Workstation T5600, 825W Tower

Genuine Windows 7 Professional 64-Bit Operating System DVD

Processor: Intel Xeon Dual Six Core E5-2620 Processor (2.0GHz, 15M, 7.2 GT/s,Turbo)

2GB NVIDIA Quadro 4000, Dual Monitor, 2DP & 1DVI (max resolution 2560x1600 two)

8GB, DDR3 RDIMM Memory, 1600MHz, ECC (4 DIMMS)

PERC H310 RAID Controller

256 GB Solid State Drive

500 GB SATA, 3.5 Inch, 10K Hard Drive

8X DVD +/- RW Optical Drive

English  Keyboard

Dell USB Optical Mouse

Precision T5600: 3 Year Basic Hardware Service with 3 Year

$2,029.00 Dell Outlet       + $180 4TB external USB3 Disk  $316 32GB ECC memory  Total $2,525,00

My Wife Dell better then mine less then my son's  purchased in  2016

Dell Model: T3620

Processor: Intel Xeon E3-1270 V5 3.6 GHz 4 Core

Ram: 32GB 4X8G 2133 Non ECC

Storage: Solid State Drive 512GB

Graphics: Nvidia Quadro K2200

Removable Storage: Dvd+/-Rw 16X

Operating System: Windows 10 Pro

$1,934.32 Dell Outlet.

Not all features in Photoshop can be multi threaded.  Some processing is sequential in nature.  Many feature will take advantage of all the cores you have I have seen things like smart blur peg 24 threads on my system.   Some features also will use you GPU you do not need the greatest Display adapter unless you also use Premier Pro or are a Gamer they will work better with top of the line Display adapters from Nvidia.

Picturequest  wrote From my research PS and Lightroom really don't take advantage of all the cores.

I keep hearing that all the time, but when I look I never see anything to support it. Seems like a persistent myth to me.

Here's an i7-7700K and Lightroom CC going crazy with the sliders, on 36 MP raw files:

I built this system about a month ago (with an M.2) and I'm impressed. Never seen Lightroom performance like this before (Photoshop has always behaved well, no matter what hardware I put it on).

I also have another machine at work, an older i7-3820 (SSD not M.2). Core utilization is just as good there, although on the whole a tad slower with Lightroom.