Will one of you guys who are running at 300 mem clock and worksize=256 give 225 mem clock and worksize=128 a try, and let me know your before and after results.
I don't have any 5830s, but all 58xx cards should behave similarly. On my 5870s I noticed that below ~250 mem clock worksize=128 works better. In fact, the optimal settings I've found we're at mem=186, worksize=128. That gives a few Mhash/s more than worksize=256 and mem anywhere between 250 and 400.
The conclusion I came to with the 6870 was that the
sweetspot was between 180 and 240. I was thinking the 5800s should be similar. There seemed to be a nice spike between those values, then
below 180 the hash rates fell off rapidly. Did you find a similar pattern?
Pretty much spot-on. At worksize=128, between 180 and 250 the hashrate varies by a couple Mh/s, below 180 it drops fast and above 250 it starts decreasing slowly. By mem clock 300, worksize=256 is ~10 Mh/s faster and peaks at mem clock 354. But the worksize=256 peak @ mem clock 354 is still about 5 Mh/s lower than the worksize=128 peak at mem clock 186.
If this is not a dedicated rig though, then there is one issue with using mem clocks as low as ~200. Any load on the video card, such as playing video or flash, will lower the hashrate a lot more than at higher mem clocks.