This is what Im doing for voltage:
1.4v for 24/7 and stick to 100 bclk
1.52v for 3d and CPU intensive benches, bclk oc ok
1.62v for 2d, PI and pifast only, bclk oc ok

Also, there is no need for excessive stress testing, that is just asking for trouble with these chips. Run LinX or similar for an hour, chances are you will be fine with that.

I have a 5.7+ Ghz chip and no degradation at all thus far with the above.