Although you have fitted an aftermarket cooler I think you got lucky.
My bfg oc with stock cooler hits 740/1756/1940 max and not a heat issue I think. If I put the memory to 1950 even with the card running cool at idle with 100% fan, it artifacts and crashes immediately.
If I set the shaders higher than 1756, it crashes in 3dmark in about 10 secs with temp of card hitting 60 degrees.
If I set shaders higher than 1800 at idle it crashes immediately.
So well done on your results and count yourself lucky you have a card which would appear to be the fastest overclocked GT I have ever seen (on several forums) by a long margin.(looking for jealous smiley but can't find one

)