It's all in the RetroNX Discord. As far as I know all Mariko Switches with Samsung or Micron RAM can reach 1996.8MHz without overvolting (which isn't supported on Mariko either). Hynix can only barely reach 1800MHz (so about 1790MHz or so).
got it, it works
I kept the standard clock in sys_sdrammtc.c (1862mhz) and right now it loops in memtesternx.nro to see, if its stable