Perhaps your card cant handle the overclock? Have you thought of that. Every chip is differnet some clocks better others dont. Use MSI afterburner and increase the power target 110 see what chane it brings and then 120 ( if the slider goes to 150 doesnt mean all card can use that. ) then 20mhz increase in base clock and then another 20MHz. Memory 100MHz than another 100MHz so you will know your limit. Each time Play very high quality games for few hours see if it last. Run Vantage/ 3dmark etc.
This should give a better understanding of your particular cards overclocking capability. No overclock is 100% stable though.
The Mem test site got the full instruction on how to use this and other ways to use it, its time consuming I know but gives you peace of mind.
Thanks