What amount should I overclock the pi3 for good performance?
That depends a lot on the game. Some games, not even overclocked the RPi3 will run at full speed. You need to test.
Also what temps would overclocking it give?
Sorry, but I don't have this information.
Overclocking is a useful and valid feature, very common among users, but I can't guarantee it won't affect your Rpi. Overclocking has a risk, so the user has to be aware of the risk and do it on their own, always remembering to have a fan to ensure that the RPi will not overheat.