Stale shares are shares for a block submitted after the next block is already being mined. Its result from network latency and fast block times and has nothing to do with memory errors or overclocking. Too much overclocking can definetlly cause memory errors and invalid/rejected shares though. Some of my Powercolor 4GB Red Dragon RX 570's run stable at 29.5-30.5 MH/s with a 1150 MHz core and 2075 MHz memory clock. I do have some that will only run at 1950-1975 MHz memory overclock at ~28.5 MH/s.
for me too
i have msi rx 570 gaming x 4gb elpida and i cant increase memory higher than 1950 system goes to crash and i get 28.5 mh/s
and my friend have same card az me and same windows and driver but he can go memory to 2100 and get 30 mh/s
just 1 diffrent with my card and my friend is asic quality for me 76% and for he is 67%
And now, with the warming of the air, I had to decrease memory to 1900 because my system crash after 4 or 6 hours to work.when i go to 1900 its work fine but my hashrate go to 28 mh/s