Argh, damn mobo.
Its 50% 50% if it finds my 12GB RAM or only 8GB when booting. Im going to RMA this board.
Did you try this 12 Gigs of memory is only supported at 800-1333Mhz. Some users can run 1600Mhz successfully with some voltage tweaking but 1333Mhz is the max supported speed using 12 gigs on a X58 board.