Keep increasing clock and/or memory frequency by 5mhz and test it with 3dmark. if see anything wrong reduce it to the speed it was running fine. I increased my 3dmark score by 1000 after overclocking, but honestly I think no one would be able to notice the difference with their physical eyes.
if your also using an MX verson, it would be useless to OC it, you usually see the frame rate increase when you OC the Geforce titanium versions(Ti) but you can still try OC'ing the Mx.