The Memory has various groups of settings which are preprogrammed into an area of the memory which the BIOS can read. The MoBo is selectimg the default 1.5v JEDEC profile which id 1600 Mhz (see your last image)
798.1 x 2 =1596.2 MHz
If this is an Intel build, just go into BIOS and load XMP profile...
But remember ...
Ya want to install RAM in matched pairs on most boards (in 4's for X99 / X79)
You don't wanna mix RAM sticks w/ different specs