overclocking a MSI NX7300LE

i want to overclock a nvidia graphics card, a NX7300LE. Display Properties has a tab called "MSI Clock", which allows me to set the clock on the 2D, 3D, and memory speeds. what is a safe overclock speed that could be achieved? right now the card is running at 115 F (normal), and the highest that it usually gets to (when playing 3D games) is 120-122 F. the clock settings right now are at 450MHz (450MHz default, 600MHz max) for the 2D clock, 450MHz (450MHz default, 700MHz max) for the 3D clock, and 648MHz (648MHz default, 9860MHz max) for the memory clock.

what is a good overclocking speed, and what temps are too high?