well technically the high freq chips right now are out of spec and overclocked. people just don't care because chances are good that they work. XMP/EXPO are overclocks but people treat them like standard settings.
so it makes sense that current IMCs and boards are struggling with these speeds since they're far out of the spec they were designed for years ago.
look at the SRAM specs on the loongson.
there is no way it is getting those performance figures unless they've created the fastest SRAM on the planet.