If you have an Nvidia card, you should also overclock the Shader Clock. Select Reset in afterburner to reset the Core Clock to factory defaults and move the Shader Clock slider in Afterburner in 10MHz increments and follow the procedure explained above. Once you find the stable frequency, set your max Shader and Core frequencies and check for stability. If not stable, reduce in 10MHz increments the shader clock and/or core clock until the GPU is stable.

Overclocking the graphics memory
Just like core and shader clocks, you can overclock the memory to. Select Reset in Afterburner and simply move the slider Memory is the nvidia rtx 3090 worth it Clock and do the same procedure to find maximum stable memory overclock. Once done, set all values - core, shader and memory clocks to the values you just found and do the stress test again. If the card is not stable, you may want to reduce the memory, core or shader clocks to get a stable overclock.

Benchmarking
If you want to see if there is any difference in performance overclocking, you can check that with 3D benchmarking applications like trial versions 3Dmark '06 or 3D Mark Vantage. You can also download and install FRAPS, an application to show the frames rendered per second in a game to see the difference in gaming performance.