Each card is different. Start by downloading a graphics card benchmarking software
Then add 50+ clock speed and run the software. If it runs fine no lag spikes add 25 and and add 12mv and keep doing this over and over till you get your max stable clock. It's not hard just time consuming good luck

Do GPU Clock 1st then add memory I would start at 300mhz I feel that's a pretty basic reliability for our cards. I personally wouldn't go over 500 mhz bc of heat reasons