Yes, but by one notch at a time, and then test again. keep doing that until there are no artefacts. Watch the heat. Monitor the GPU with MSI afterburner or something.
Make sure to test though.
Read a good guide on GPU OC'ing get familiar with what you are doing. You may want to increase the power too, and not adjust the voltage to begin with. Read about it, and be sure what you are doing and how to measure the affects of the things you change.