How many GPU cores does a MAC need to use Illustrator and Photoshop

Here are some suggestions from Adobe for GPU issues.

https://helpx.adobe.com/photoshop/kb/troubleshoot-gpu-graphics-card.html

I hope this helps, perhaps it has some tips for you

neil barstow, colourmanagement net :: adobe forum volunteer:: co-author: 'getting colour right'

google me "neil barstow colourmanagement" for lots of free articles on colour management

Surprisingly - it's more about the CPU than the GPU - if you have a 4k display then more cores possibly better in the GPU.

Photoshop can operate with a low-end GPU - most onboard graphics use between 512-1024mb of Memory which is fine for a 1080 screen. 

It's the CPU that requires a bit of oomph and plenty of Scratch Disk space for Photoshop - so a larger Hard Drive is preferred. 

https://helpx.adobe.com/ie/photoshop/using/scratch-disks-preferences.html

If you can afford all the GPU cores then go for it.

But in terms of the CPU - Photoshop and Illustrator top out at about 8 cores - after that more cores are not going to help.