No, the 1866Mhz RAM won't fit in a 1600Mhz slot.
No, the 1866Mhz RAM won't fit in a 1600Mhz slot.
The Asrock B85 Killer Fatality supports LGA 1150. The memory card states compatibility with 1333Mhz/1600Mhz. Will it function at 1866Mhz? You have a HyperX Black 1866Mhz 16GB with two 4x4GB modules. You want to test it in the mentioned memory module.
It should function well around 1600MHz. The chip includes a "QVL" feature, a vetted vendor catalog containing verified working memory units: https://www.asrock.com/mb/intel/fatal1ty b85 killer/#Memory. They highlighted several 1866MHz kits, including some from Kingston HyperX, noting the system can operate at up to 1600MHz.