The potential to overclock on a number of identical cards can be very different. It's the same situation as CPU's. Some will fly and overclock dramatically, others won't. I can only provide results for the card I have in my possession and though it gives a general idea of what to expect, your results could be higher or lower. Its pot luck! This particular card overclocked to 600/590 which is way beyond even the stock X850XT PE! The memory that is rated at 1.6ns should have been able to hit 600Mhz (1200Mhz) but it couldn't. This leans me to believe that ATI are most likely using aggressive timings above the Samsung 1.6ns specification, but I can't be sure until I test more X850's.