I currently have installed a 64GB HyperX kit ( https://www.amazon.com/gp/product/B06XNPSZY4/ref=oh_aui_detailpage_o04_s03%3Fie=UTF8&psc=1" rel="nofollow - HX426C16FBK4/64 ) which appears to be working just fine, but am no expert when it comes to QVL lists and cannot determine the question (1) of whether or not it would be possible to add a second of the same kit to achieve 128GB. I built systems back in the day but specs/considerations appear to have changed significantly and are more sensitive these days.

If I'm unable to add a second kit, I see that the HyperX Predator - https://www.amazon.com/HyperX-Predator-3000MHz-HX430C15PB3K8-128/dp/B072QBZ2H5/ref=sr_1_1%3Fie=UTF8&qid=1530646434&sr=8-1&keywords=HX430C15PB3K8%2F128" rel="nofollow - HX430C15PB3K8/128 is listed as compatible at 8 x16GB. If that's the case, a question of mine (2) is if only half of this kit could be used for 64GB? Then, if that's the case, (3) how do I go about finding this same stick available in a 64GB kit since the product number itself denotes a 128GB kit? 

I'm losing sleep over this specific question and would REALLY appreciate an expert opinion.

Current Build:

X399 Taichi - https://www.asrock.com/mb/AMD/X399%20Taichi/index.asp#Memory" rel="nofollow - Memory QVL

1900x AMD Ryzen Threadripper - https://www.amazon.com/gp/product/B0754JNQBP/ref=oh_aui_detailpage_o04_s02%3Fie=UTF8&psc=1" rel="nofollow - LINK

64GB Kingston HyperX RAM - https://www.amazon.com/gp/product/B06XNPSZY4/ref=oh_aui_detailpage_o04_s03%3Fie=UTF8&psc=1" rel="nofollow - LINK

4x 2TB FireCuda HDD - https://www.amazon.com/gp/product/B01IEKG2HM/ref=oh_aui_detailpage_o00_s00%3Fie=UTF8&psc=1" rel="nofollow - LINK

try changing the product number in part code from 128 to 64

but !

theres less chance that 8 sticks will run at same or similar speed and timings and EASE that 4 sticks will run