intel and memtest doesnt stress enough on vdimm.
i can run lower vdimm and vtt with it.

try this so far the highest stress and will show errors

run prime95 25.9 64bit set large fft and then set custom, change run fft to to max mem around 5.4gb in diagnostic mode
if hang ( could be either ioh/ich voltage or inssufficient vtt)
if more than one thread error.. insufficient vdimm
if one thread error vtt insufficient or vtt/vdimm ratio wrong ( one of them is overvolted or undervolted)