Not sure how deep into it you went, but I found with 4 sticks I had to bump soc voltage, memory voltage, and loosen all my timings, especially tRFC. I can only pass training at marginally higher mem clocks with tRFC around 350ns with 4 sticks whereas 2 sticks was down near 200ns. Is it perfectly stable though... I think it's crashed once in the past month? So not perfect but it passed 12-24h of every stress test I could think of, and the one crash was near idle which probably just means my voltages need another bump.