Please try using lower vccin!
In my quick testing, 5200mhz can run 32m at 1.500vCore 1.600vccin on air cooling. 1.700vccin hangs, 1.800vccin hangs, 1.900vccin hangs. Seems a good starting point is around 1.5 to 1.55.
You must keep vccin atleast .080v higher than vcore or it will lower your vcore under load.
Havent tried this theory yet on ln2 but its working on air so far.
Sharing in hopes that others will try it, post results below!