Update on adventures in 128gb land. Options were:
KIT #1: 2 x 64GB = 2 x F4-3200C14Q-64GTZR. (DDR4-3200, CL 14-14-14-34 1.35 V)
KIT #2: 128GB = F4-2933C16Q2-128GTZRX. (DDR4-2933, CL 16-16-16-36, 1.35V)
KIT #3: 128GB = F4-2933C14Q2-128GTZRX. (DDR4-2933, CL 14-14-14-34, 1.35V)
The 128gb kits are no longer for sale, but you can see the sales page for my kit #2 here: https://www.newegg.com/Product/Product.aspx?Item=N82E16820232631
. Kits #2 and #3 were offered to me by Gskill tech as X399-specific kits, and Kit #1 was just a few 64gb kits at 3200mhz put together. I tested kits #1 and #2, having tested #2 before it vanished from Newegg. #3 already wasn't available at Newegg at my time of purchase. Gskill later confirmed that the SKU no longer existed, and wasn't just out of stock. And now, two days later, Kit #2 is listed the same way. Interesting, but why? More on that later. Lets look at how the kits behaved.
Both kits are Samsung B die, and some will recognize the first as the 64 gb version of the 32 gb kit everyone is recommending in the forum. Sequentially booted 1,2,4,6,8 sticks of each kit, cycling from 16gb to 128 gb. Both kits provided full 3200 Mhz speed up through 4 sticks. Yes, that wasn't a typo. The 2933mhz kit was working and stable at 3200mhz simply by using the 3200mhz timings. Wait, could Gskill be using faster RAM in these kits and just be labeling them 2933 for some reason? Hmm...
Once 6 sticks were used, everything dropped back to 2933 mhz. Using all 8 sticks, the 2933mhz Kit #2 was working basically "plug and play", dropping them in and using D.O.C.P. But the 64gb x 2 Kit #1, to replicate the same speed at its slightly advanced timings, required using D.O.C.P., then pulling back the Memory Frequency to 2933 MHz.
So Gskill's logic in creating the #2 and #3 128gb kits for X399 makes more sense. Accepting that 2933 Mhz was simply the highest possible stable memory clock for 128 gig to work properly with infinity fabric, Gskill may have just tried to save the user the time tinkering, set the kits to 2933 MHz, but used better Ram to ensure a very easy process for the 128 gb buyer.
Ok, if that's the case, then why drop the kits? Why are those two SKUs now unavailable? It could be a few reasons. They weren't selling enough of them at 1500 a pop, or users were balking at paying an X399 premium for 2933mhz memory, when 2 64 gig kits of 3200mhz memory was only $40 more, a pittance in the 1500 range. But buying 3200mhz memory to fill 128 gb on X399 is simply wasting money, because it cannot and will not reach those speeds due to limits of the Ryzen architecture.
So which way do you go? Well, testing showed something interesting when I benchmarked Kit #1 at 2933mhz with its C14 timings against Kit #2 at 2933mhz, also using the C14 timings, not its native C16. Using AIDA64 memory bench (averages (SD) based on n=5 runs):
Kit #1: Read: 71793.8 (280.82), Write: 74122 (697.32), Copy: 73288.6 (291.41), Latency: 97.36 ns (.149)
Kit #2: Read: 71002.2 (420.20),Write: 73735.4 (387.57), Copy: 72521.2 (437.84), Latency: 101.36 ns (.287)
Not really surprising, the faster binned memory performs ever so slightly better than lesser memory operating at the tighter timings. And so the question of why 128 gb 2933gb kits were quickly made extinct by Gskill has an answer: no one in their right mind would buy them. Buying them is essentially saying you are accepting reduced performance RAM (2933 MHz) for ease of configuration over usability beyond the life of the X399 motherboard. In other words, once you move 3200mhz memory off X399, where the 2933mhz limit imposed by infinity fabric no longer applies, all the performance typical of fast RAM will be present. The X399-specific Sku's seem to be slightly better than their listed timings, to ensure a strong chance of plug and play operation. I kinda wish I could get a hold of the C14 2933mhz kit, to see how tight the timings could be pushed.
TLDR: If you want 128GB for your X399 board, buy 3200mhz C14. Avoid any kits rated at 2933mhz.