RoEy, ditch the 20 multi mate and go 19 multi, will be far easier to stabilise (and strangely enough with lower volts).

Try to run first Custom with 20-20K set to see if the Vcore is sufficient, then go blend and work with VTT voltage... if that passes after a few hours, try Hyperpi 32mb with 8 threads, and play some more with B2B Cas delay and VTT voltage...