What component priority when upgrading PC? (Houdini, zbrush, mari and vray focus)

ISUther

This is what i have at the moment. 

Motherboard Name Asus Rampage III Extreme (1 PCI, 1 PCI-E x4, 4 PCI-E x16, 6 DDR3 DIMM, Audio, Gigabit LAN, IEEE-1394) 
Motherboard Chipset Intel Tylersburg X58, Intel Westmere 
DIMM1: Corsair Dominator CM3X2G1866C9D 2 GB DDR3-1333 DDR3 SDRAM (9-9-9-24 @ 666 MHz) (8-8-8-22 @ 592 MHz) (6-6-6-16 @ 444 MHz) 
CPU Type HexaCore Intel Core i7-970, 3200 MHz (24 x 133) 
Video Adapter NVIDIA GeForce GTX 780 (3 GB) 
Disk Drive OCZ-VERTEX2 ATA Device (SATA-II) 
Disk Drive WDC WD1002FAEX-00Z3A0 ATA Device (1 TB, 7200 RPM, SATA-III) 

Ofcourse there is also SSD and HDD drives and case 
(Coolermaster Cosmos S). 

My question is: 
If focusing on 3D Houdini, zbrush and Mari
what components are most important to upgrade?
When getting 128 gb ram does int make a lot of difference when having 64bg for example?

If you make priotirity list what is speedning up the rendering most?
When using Mantra for example. 
For lighting vray. 

CPU?
RAM?
Graphics card?

As i understand i need to upgrade Motherboard, CPU and RAM. 
What would you sudjest? I have max 2000 euros

What do you think is x99 motherboard good idea?
https://www.vortez.net/articles_pages/gigabyte_ga_x99_ultra_gaming_review,1.html

And what cpu would you recommend?

ZacD

Generally, more ram doesn't increase performance unless you are maxing out your available ram. Just get 16-32GB with room to upgrade as a starting point. It's super easy and quick to add more.

Houdini does have some GPU acceleration, for Pyro FX and Fluid simulations, so a better GPU with more vram would be a good idea. More vram is a good idea in general for high resolution displays as well. 

Vray and Mantra are CPU based renders, so get the biggest CPU with the most cores you can afford. That is probably your first priority, probably the 6800k, but might also want to look at AMD's latest offerings and the 1800X, which is a faster chip on CPU benchmarks, but I'd want to see actually tests in Vray and Mantra if you can find any. 

ISUther

Currently i am between 2 options. 
1 is to upgrade my pc
2 is to buy Wacom Cintique 27 QHD 

Thinking what would support my path in the CGI field more. 
I do like to sculpt but same time i like also VFX in houdini.

hard decision 

ISUther

As i understand Mari works like this that you paint textures and then you bake it. 
As i am noob in Mari i would ask: 
1. If i texture would you able to bake for example 6k textures with 6gb ram pc or will it be insanly long time?
Note! My houdini renders some of them rendered One week

Dataday

With Mari, you need a lot of VRAM. Also because Mari caches everything to disk as you work, the faster the ssd you have it installed on, the better the performance. For that, going with a m.2 ssd is going to be a good idea (if you have the funds for it). Most new higher end motherboards will have an m.2 slot.

VRAM you get from the GPU. Thankfully, due to VR taking off... it put pressure on GPU manufacturers to increase the VRam size in order to pave the way for VR content. The Nvidia Geforce 1080 Ti is one of the best options right now for that.

X99 motherboards rock! Same with the intel CPUs that go with them. Its what I personally use as well.

CPU is going to be the primary driving force for Zbrush and Houdini.

Since this is going to be a hefty upgrade, I would recommend going for better components than a cintiq. A normal tablet still works wonders, in fact I still find myself going back to an old intuos 3 tablet over my own cintiq more often than not.

ISUther

I got information from my friend who is actually working with one PC game. 
He told me that i can handle 2k maps in mari with my 6 gig but when more then 2k maps it is going to be pain. 
As people see stuff differently and describe fast and slow differently (as for one 100km/h driving is fast and for some one else it is slow)

If you take a look at this: 
https://www.youtube.com/watch?v=j4h-VaXcpL8

I have no idea what maps were used there and i have not started to learn texturing but with 6gig ram is it almoust impossible to texture?
I got info that at first you paint the textures there and then u click "bake" button and it will texture. 
So if i gor example have 8k texture does it bake it for week with my 6gig ram?