First of all disable DRAM static read, enabled makes your ram unstable at OC...
Then try to set transaction booster enable, Boost level 2 or 3 (see where you Get), this increases your ram performance.

Redo your TEST to find the max fsb can handle your mobo - cpu and if you want TRY also multi X9 to relax FSB on chipset....

400X9 = 3600 MHz also but your chipset may run cooler....
I have maximum stability when NB never pass 1.41V...