Apologies for jumping in, just want to help.
I happen to have ( and do not sell ) the same mems Albrecht has.
Both on Apex VI and Rampage VI Extreme ( which is an 8 slot board ), I never had any issues running them at 4000 / 12-12-12-28-1T tight, with 1.85V rock solid.
I have them installed on my main PC ( daily ) with an I9-7980XE, and they do 4000 / 15-16-16-36-1T with 1.50V for daily use.
Not playing Devil's advocat, but if you not take them ( dirt cheap price offered here ), I might consider buying them and go to a 64gb setup.