I5 750 oc

hi
im currently trying to overclock my i5 750 to 4ghz right now

i've set my baseclock to 200
multiplier 20

vcore 1.35
vdroop low

the problem is that after 30 mins of prime95 1 core fails

i've read online that in order to stablize my cores, i should increase my cpu vtt

my default vtt ix 1.12
and i tried to increase the voltage a tiny bit.
the problem is when i even increase it to 1.2
the cpu is no longer stable

i cant even boot into windows. and even to post bios may freeze

my mb is a msi gd80

thanks for reading