Memory manufactures and some motherboard manufactures will say that you need to buy all your RAM as one tested kit... Another words you would need one single kit that included 128GB of RAM. However in my personal experience I have not ever had any issues with using RAM from different kits as long as all of the specifications match... In your case I am not sure you really have a choice as I dont think Corsair makes that RAM that TiN is suggesting that you use in a 128GB kit.... so yeah... lol.   

jasoncodispoti
Memory manufactures and some motherboard manufactures will say that you need to buy all your RAM as one tested kit... Another words you would need one single kit that included 128GB of RAM. However in my personal experience I have not ever had any issues with using RAM from different kits as long as all of the specifications match... In your case I am not sure you really have a choice as I dont think Corsair makes that RAM that TiN is suggesting that you use in a 128GB kit.... so yeah... lol.   

Thank you again! I understand why they would say that and why in some situations that might be the case but I figure in majority of situations that would be actually against design that is supposed to make things work together. And my likelihood of being fine should be higher by ordering them both at the same time straight from Corsair.
 
So I just pressed ‘buy’ button, 128 GB here I come, fingers crossed …
 
Now I just need to figure out which M.2 2280 to go for and I should be ready to start putting it together.

Ignore. Can be deleted. 

Quick update now that Jason has bumped the thread: My X299 Dark didn't have problem recognizing 128GB. I didn't do stress test yet but I am getting closer to that point.

LOL, I thought I was replying to one thread and after I posted realized that I was on the wrong thread. Thanks for the update on the RAM! Can you post links to the RAM that you ended up purchasing in case someone else comes along looking at this?  

jasoncodispoti
LOL, I thought I was replying to one thread and after I posted realized that I was on the wrong thread. Thanks for the update on the RAM! Can you post links to the RAM that you ended up purchasing in case someone else comes along looking at this?  

I've purchased qty 2 of this: https://www.corsair.com/us/en/Categories/Products/Memory/VENGEANCE-LPX/p/CMK64GX4M2C3000C15

To clarify - G.SKILL DC DIMMs are not compatible with Dark boards. Those are poor overclockers anyways. That however does NOT mean that proper G.SKILL 16Gbit-based 32GB modules will not work, these will be fine and 128GB capacity is supported with such modules.

MemTest86 returned errors within minutes :( Now I am repeating test with only first two slots populated.

May have to change the timing (increase numbers) to allow these 2 sets to work together

Cool GTX
May have to change the timing (increase numbers) to allow these 2 sets to work together

That is one of reasons why I am now testing only one set at the time, to try to figure out is one kit defective or it is me trying to use two or something else.