I just bought a Gigabyte Radeon HD 7950 GV-R795WF3-3GD.
Upped the GPU Clock to 1100Mhz (which is the maximum) from the control Panel.
I am getting 550Mh/s at average.
Now I am a bit curious what I can do with the Memory Clock.
Is it good to lower it? And if yes to what extend?
A few notes. Enable manual fan control, or use --auto-fan if you are using cgminer or bfgminer. In my experience if you OC the card that high and then leave it up to ATI/AMD drivers to run the fan you are going to cook things. Set the fan to 75% and your cores will run ~20C cooler.
Second, underclocking the memory clock speed in the ATI Control Panel will most likely look like it works, but not actually take effect. Use something like
GPU-Z to see what your memory is actually running at while mining. If you want to underclock your memory, you'll need to use
Afterburner along with a few manual tweaks found in
this thread.
Right now I am using Afterburner to run my 7950's at 1175 core, 200 memory, stock voltage with 75% fan speed using the 12.8 drivers. They run at about 60C and are very stable doing 600 Mh/s a piece.