I guess it's the getting the bandwidth of the RAM maximised in a way the the GPU is smoothly and constantly fed with data. Not sure why, but anything other than 1500 or 1800+ RAM is rubbish on R280X.
I think thats not true because either the memory or core waits for the other unless they are timed perfectly.But whatever waits doesnt make a difference if the clock rates are equivalent to what you are comparing.THE REAL REASON IS: bad memory latencies/timings. They are coded as different values for different speeds and they very often are suboptimal.
how can one find out better than that?