Don't oc your memory clock, it will make little to no difference. Ocing your core and shader will help the most. You need to enable the user defined fan control and change your fan arc in the settings menu under "fan". Your spike should typically be 1% fan for every 1degree celcius up to around 70c or higher if you can stand the noise. Fan profiles are key to keeping your gpu cool and ocing will run you a little hotter.
the OC you currently have is pretty nice for that card, you might be able to squeeze 800/1900 out of it; If you start getting random crashes with loss of signal while gaming it is most likely your voltage, which you can also adjust in afterburner; just dont go too high you might fry your card. 10mv bumps until its stable is the usual rule of thumb. if you start getting artifacts, it is more than likely your shader is too high, and back it off a bit. always double check on what other people are running their clocks and voltages at so you can compare and not over volt and fry your card, or clock too high and start throwing artifacts.