Thanks for the reply Vr2Io but i just worked it out.. kinda
i disabled 14 of the 16 dim slots via bios and its now freaking fast!
Its a beast of a server brand new Dell R750, dual 6330, 1Tb memory, 10 x 1.92tb NVME, 2 x 9400-16e talking to 12 x 16tb, 8 x 10tb
can work with 128gb mem for the moment, just been without for 2 weeks so keen to get everything set back up! once online ill then start playing with the memory config as i think its a server issue.. while dell shipped the server with all memory populated in the first 8 dimms and dell can "optimised" thats not the actual channel config.. ill change the memory into the channel groups when i get back home in a couple of weeks..
idrac has been so handy while building haha