Why would overclocking make no impact that doesn't make sense.

Setting your memory clock higher directly increases the hash rate.  Your afterburner settings are not working make sure you are applying the settings before launching the miner.

Download a tool called Hwinfo64.

Install and choose sensors only mode.

Scroll down to your GPU's and look at GPU clock and GPU Memory clock. They should match the settings you have in afterburner, if they don't then you aren't overclocking the card.

Make sure the temp stays between 60-70*C and make sure your GPU Memory errors are either 0 or very low, like 10-20 every minute.