You need to run prime95 for 24 hours to make sure it's 100% stable. I nor anyone else can tell you when you're pushing it to much, you can pretty much go as high as you want until temperature or stability becomes a factor.
I personally am not afraid to put as much as 1.9v through the core if need and if temperature allows it.
Intel C2D E6320 / AMD Athlon X2 3800+
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