bronan, I can confirm your memory speed theories. My 7970 is unstable if I set the memory slower than stock. My rig crashed 5 times a day until I experimented with putting the memory at the stock speed. The rule of -150MHz from core clock doesn't apply to this card. Wish it was like my 5830's where I can set the memclocks at 300.
Haha yes both my sapphire 5870 vapor x went to the usa but where perfect able to run at 0.900 volt 750 mhz on core and 166 mhz on the memory
They are still awesome cards and i think the new owner is very happy with them.
I remember i often bend over towards my computer to make sure they where running fine
( so silent )
And yes i could game on them also while mining with no problems ofcourse not with the graphics power of these but still.
Do not get me wrong the 7970 i have now are monsters and i love them but underclock/volt wise they are a pain in the ass they just want speed and more speed
So a bit underclocking is possible but not much, undervolting does not work either, so far it seems that the cause of all this is ELPS the advanced power save build into the cards. This far i have not been able to turn it off completely i would like that though so i can proof if my theory is right.
Maybe someone has advanced knowledge at ati bios matter and would like to help find out if its possible to turn it of by flash the bios with a alternative one