OK...so I just purchased 2 of the aforementioned cards from NewEgg at the same time. After they arrived I installed them and started guiminer. Both were running around 317mhps at 800mhz clock speed.
Here's where it gets interesting. In CCC, one of the cards allows memory clock settings from 625mhz - 1325mhz. The other card only allows 1100-1325. So I loaded up MSI afterburner and attempted to further tweak the cards. I was able to get them both functioning properly at 1.2v and 900mhz which produced 352mhps...on ONE of the cards. The other card immediately dropped to 250mhps. I dialed the second card back to 1.1v and 800mhz and it jumped back to 317mhps.
In addition to this, the card that performed worse (card A) when overclocked runs a lot hotter than the other one (Card B). When they are both at 800mhz, card A is around 83c while Card B is at 72C.
Any thoughts, suggestions, input, etc would be greatly appreciated. I wonder if Card A is defective...