Mac Pro Late 2013 Upgrade

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Hey All, 

First post, so please do let me know if I have made a mistake or need to post this elsewhere. 

At work, I've been working with our Graphics designer to "Upgrade" his Mac Pro (Specs below) my manager decided the cheapest option would be to get an eGPU but now we find it's not compatible with Blender. 

Mac Pro Late 2013
MacOS 10.15 (Catalina) 
Intel Xeon E5 3.7Ghz (4C/8T)
64GB RAM 1866Mhz
256GB SSD
X2 AMD FirePro D300 2GB

I proposed the following which I was then asked, why can't we find an Windows alternative? 
 

Mac Pro Tower 2019
Intel Xeon W 3.5Ghz (8C/16T)

96GB RAM 2933Mhz
1TB SSD
X2 AMD W5700X 16GB

 

The above proposal tops out at about £6,600 but whenever I come across Designers I always suggest Mac, is this now no longer the case and is there a suitable Desktop/laptop out there based on Windows? 

Applications include: 

Blender (Rendering/3D modelling) 
Adobe Photoshop
Adobe Premier
Adobe InDesign

We also got a Razer Core X & RX 580 which isn't supported in Blender 2.9. 

I suggested boot camp into Windows but that's more man hours than the company want's to invest. 

Thank you for any and all suggestions, I'm loosing sleep on this project until I can get it sorted