GPU keeps crashing help

Well when it boils down to it I have an Corsiar 850tx 850watts with an EVGA gtx 275 ftw and I've been trying out their precision application to make it easy for not so tech savy people like me to overclock. So i tried giving this card some extra overclock. So i looked around the internet and got a feel for what to do to see what my maximums where. So I used furmark and increased the clock speeds of each clock one at a time till i got a crash then back off a bit. then tried it with all of them up. with furmark still running in the background baking the card up. it went good no crashes no artifacts. But then when i play a game like Empire total War or Crysis the GPU kicks me out of the game. At a milder overclock it works fine. So i don't really know what's up sometimes it'll kick me out of the game and i'll quickly look at precision and temps didnt' even get that high only like 60C. So does anyone have any suggestions

well the thing is when I'm using a stability application it does just fine at those max settings. but it only works at a mild overclock in actual games

That's what I was thinking that it wasn't stable but i just wasn't sure why it didn't crash in the stabilty test but then crashed in the game