Originally Posted by Riznarf
and although it passed the stress test I got a score lower than stock...any ideas why???
It sounds like you passed one stress test but you failed the 3DMark 11 stress test. Every GPU, or even CPU, has a maximum limit. This limit can vary depending upon the configuration (cooling, voltages, drivers, etc...). 1.075v might be more than the card can handle reliably at your ambient temperature, even if the card's reported temp is in the safe zone.
It could also be the card's memory that has hit it's limit. At 800/2000 you may be generating 30GB/s (random number) of memory bandwidth, but at 850/2000 you might be generating 40GB/s (random number) of memory bandwidth. As you increase the GPU speed it increases the memory bandwidth but there comes a point when the memory chips become saturated and the extra bandwidth just congests the memory busline. This can result in a lose of performance, just like your experiencing.