Got a weird thing going on here, I have a Sapphire 5970 OC Edition and an XFX 5970 Black / Limited Edition in the same system. The first core of the Sapphire underwent some sort of thermal damage and is now unstable in the >300 MHz ranges, I have also discovered that the other GPU's aren't fully loaded when running in the same instance as this damaged GPU, so I keep it running in a separate instance of cgminer with dynamic intensity. Now, the first and second GPU of the Sapphire show up as core 0 and 3, the XFX GPU's show as 1 and 2 in cgminer.

If I provide comma-separated engine values, it seems to take the same (lower) settings for both cores on the Sapphire 5970, or maybe it's interpreting the values I provide in reverse. The XFX card doesn't respond to my settings, it reports default overclock values for the card. All of these are clocked with AMDOverdriveCtrl (I have no choice, as the rig will crash if core 1 on the Sapphire goes over 300 Mhz). So far, I am blessed though with the auto fan control, which bypasses the Sapphire's shitty stock fan control. Go cgminer! On the XFX though, fan control is also acting weird, here the default algorithm seems to do better, and if I shut down cgminer with auto-fan enabled for the XFX, then the fan on the XFX will also quit until rebooted. No more toying around for me.