Stock EXPO II settings allowed a pair of these to run at 6000MHz but with all four, it ran at 4200MHz (standard JEDEC was 5600). Managed to tweak up the voltage and it ran up to 6400MHz, but opted to bring it back down to 6000 for stability, and until I find some time to further test at higher speeds.
Any thoughts and suggestions are appreciated.
P.S. This is workstation (yes, real "work") that I also game on.