Another thing, Sims 3 was really heating up the video card. I was seeing max temps on my GTX 275 card of 83C in game.
I was getting close to 200fps in game at max settings and 1600x900 resolution.
I saw on the Sims 3 message board to enable vsync on the game (TS3.exe for Sims 3 or TS3EP01.exe for World Adventures) via the NVidia control panel and it would keep the card from getting so hot and maybe causing crashing.
After enabling Vsync it stays constantly at 60fps and after my wife played a few hours the max temp was 56C.