Core clock should be use to lower the load on memmory but should never get over +150, and this also lower the power to get the card running between 80 and 100 watts with reduced power limit between 50 and 60%
Here you have a good guide how to overclock nvidia cards
https://mining.help/nvidia-ethereum-mining/In my opinion the guide above (and other guides on the web) are 80% great but inaccurate at 20%. A great start for newcomers - it helped me to get the whole picture when I started to build first rig, but inaccurate at many aspects and details.
Advice: Proceed with caution.
Again: My personal opinion.