Sorry my bad, I think its your drivers then. Which driver version are on?
It's the latest CCC, not the beta one.. So it's 12.8. But the driver version is 8.892.0.0 as seen in device manager.
Note: When testing FurMark in 2500*1600 resolution with 4x AA on the situation is relatively normal. Yes, there is the sudden drop of around 30 point when I go from 1250 to 1251 but after a certain range, the memory clock starts to behave in a normal way. The more I increase it gradually, the more performance I get. The score I get with memory clock 1350 is higher than what I get at 1250 and am sure about it... tested repeatedly.. And around 1400 memory clock the score is noticeably higher than that of 1250. So that's a good thing.
Though the performance increase is slow. but it's not my concern. it's supposed to be slower while playing with memory clock than doing it with core clock.
But in lower resolution like 1366*768(default resolution of my monitor), there is no certain relation between the performance and the memory clock. Sometimes the score is slightly higher at 1250 memory clock than it is at 1450!
One explanation might be, The total bandwidth increases with the increase of memory clock. And the effect of total bandwidth is more conspicuous in more demanding resolutions and/or AA turned on..(Am I right with this? Someone correct me if I'm not.)
That might be one reason I am getting relatively expected result at higher resolution and AA turned on. But still that doesn't explain why the performance would drop just by increasing the mem clock by 1 from the stock clock, it would at least remain same, not deteriorate.