Its a palit with Samsung memory. If you have Micron GDDR5 memory then you really can't clock it much higher than 4300. If you have still Samsung memory but a bad cooling solution (f.e. inno3d) then it might also only let you clock to ~4400.
I can mine with 4800 memory clock on my Palit, will check the speeds right now.
same thing can't oc above +600-700 or artifact will be all over the place, this with g1 gaming, samsung memory, what palit do you have jetstream or gamerock?