Hmm, so the anandtech article on the 5870 mentions:
The specific CRC function used in GDDR5 can detect 1-bit and 2-bit errors with 100% accuracy, with that accuracy falling with additional erroneous bits. This is due to the fact that the CRC function used can generate collisions, which means that the CRC of an erroneous data burst could match the proper CRC in an unlikely situation. But as the odds decrease for additional errors, the vast majority of errors should be limited to 1-bit and 2-bit errors.
Should an error be found, the GDDR5 controller will request a retransmission of the faulty data burst, and it will keep doing this until the data burst finally goes through correctly. A retransmission request is also used to re-train the GDDR5 link (once again taking advantage of fast link re-training) to correct any potential link problems brought about by changing environmental conditions. Note that this does not involve changing the clock speed of the GDDR5 (i.e. it does not step down in speed); rather it’s merely reinitializing the link. If the errors are due the bus being outright unable to perfectly handle the requested clock speed, errors will continue to happen and be caught. Keep this in mind as it will be important when we get to overclocking.
http://www.anandtech.com/show/2841/12Maybe with higher memory clocks some computation is delayed because the memory needs to retransmit again. This may be the reason some people see increases in performance and others don't. (some people's cards can transmit 100% at the stock speed and other people's can't)
On both my 5870 and 5850, lowering the memory clock decrease hash rate. Does anyone with these 2 cards see the opposite?
what card are you using?