I try to OC my 970 to 4.2GHz and 2000 memory

my settings:
Vcore: 1.30v
cpu-PLL: 1.81v
vQPI: 1.33v
vIOH: 1.17v
vDIMM: 1.64v

it's ok for a Hyper32M with memory 2000 and uncor to 3800 (CPU 21*200)
it's ok for a LinX with 21*200 and memory to 1600
it's ok for a Linx (and OCCT) with 15*200 and memory to 2000
but it is not stable with OCCT or LinX 21*200 and memory to 2000

What I need to increase voltage?

thank you

PS: if I drop the CPU-PLL, it is not stable (I thought it helped)