I learned graphics card overclocking test: Checking glitch by own human's eye . How can I know hidden error if I can't see tiny glitch? Is there objective way to check the overclocking error?
In general, artifacting is very noticable. Flickering textures, shadows etc. Weird colors.
I would test with Unigine Superposition and pay attention. Run it once with stock settings to establish baseline.
If the benchmark crashes or artifacts, dial down the OC.