First of all as bignastyid said, if the card is overheating it will throttle itself in order not to damage itself. However the gtx400 series ran hot, but I believe it throttles at a higher temperature than what you posted. Make sure you have good airflow, and clean your system of dust. You can also set up a custom fan profile if you wish to lower the temps.
If you encounter LAG and you are not sure if its due to your internet connection or if it is due to your hardware then I suggest you download Fraps. Fraps will tell you your fps rates.
Hope this helps!