Choosing CPU for Workstation

[Sebbbs]

Hello,

I'm a Gaming-PC building enthusiast now attempting to build a workstation for my studio. 

The PC will run Unreal Engine 4(++) where the program doesn't scale linearly with CPU cores. I will also be used for video editing in Avid & Premiere Pro as well as color grading in Davinci Resolve. So I think I'm looking for a balance of cores and clock speed. 

I will fit either a Quadro RTX 8000 or a RTX TITAN (for the memory). The build demands 128gb RAM--this is where my question begins:
I'm comparing different CPUs and have boiled down to some alternatives.

1). Intel i9-9980XE - which has high single core performance as well as high multi core performace and looks like an overall great way to go. A cheaper alternative would be the Intel Core i9-9900X which counts fewer cores. I'm uncertain how beneficial  the extra cores of the i9-9980XE are for our work load.

2). Looking at Ryzen 3000 has made me curious. The 3900X and the coming 3950X looks like great contenders to the X platform from Intel. With even higher single core speeds and great multi core performance for a fraction of the price. The problem with this platform is the RAM memory. The motherboards only have 4 DDR4 slots which makes the demand of 128gb a challange... 
I've found these 32gb sticks which would give me 128gb in total (4x32) (https://www.gskill.com/products/1/165/Desktop-Memory). My question is how these actually would perform in my build compared to using 8x16gb sticks with either the Intel i9-9980XE or the i9-9900X.

Would it work stacking a Ryzen 3950X with 128gb RAM (4x32) ? Or is there a reason I have to go with a motherboard that gives me 8 RAM slots? Like the 2066 Intel chips or even TR4 Threadripper?
What are the benefits of going with the really expensive CPUs from Intel? I'm maybe missing something?

Thanks! (and sorry if this question has a very obvious answer... )

Sebastian
 

[5x5]

X299 Intel CPUs have much lower single core performance than their desktopodels as they use a mesh interconnect rather than a ring is. The single core speed of the i9 is closer to a modern i3.

[Akira Shimazu]

well speaking of performance the Ryzen 3950X outperform i9-900k by almost twice faster.

[Brent744]

Everything will really depend on your budget. Given your options it seems your budget is quite high so I would go with the i9 9980xe. The new AMD Threadripper 2990wx is a pretty good contender but I believe the intel chip will still outperform that. Intel has been in the business of workstations much longer and their chips are designed to run 24/7. It's still too early to tell how many years an AMD Threadripper will last running 24/7.