I wanted to chime in on this thread, it's been a while since I have posted here.
Long story short - my case got escalated to apple corporate and they basically said they can't support third party displays and have decided to not proceed in fixing this issue.
The official response from engineering was that this only affects certain LCD panels (most of which are very very popular panels from even Apple's own pre-LED displays). The hilarity of it all is that the problem doesn't persist on any other Apple certified graphics card other than the 5770/5870 series. I personally purchased all previously supported graphics cards for Mac pro's and determined this only happens (reliably) on the latest series graphics cards. I offered to go to Cupertino Campus and give a demonstration. They declined.
I bit the bullet after nearly 8 months of frustration and bought a few remaining 30" ACD's (refurbed) since apple informed me they would replace the LCD panels in them if they had the problem. They don't have the problem becuase they were refurbed with modern panels that don't reflect the issue.
Apple wouldn't tell me what panels have the issue and which ones don't (certain panel revisions apparrently show this issue vs older revisions) so I couldn't ask Dell to replace with a specific panel to alleviae the problem. Dell says they were using the latest parts available for the replacements).
Bottom Line - the 5770/5870 cards (and/or drivers) have problems with nearly every type of 30" LCD panel and Apple won't support the issue unless you have Apple displays.
Apple corporate tried to boil it down to a, in my opinion, failed parallel example: Just as Apple can't provide support for every third party printer that you can buy - Apple can't support every 3rd party display you might buy. The problem here is that displays of this type don't have any driver requirements to function properly and adhere to strict specifications to work interchangably with a display interface (such as DVI or MiniDisplay Port etc.)
Too many people are having problems for this to be ignored, however, the population of people using new mac pro's with older (OLDER!? more than 6 months old !) 30" displays is a small population and Apple is copping out of fixing the issue becuase it may, in fact, be the hardware of the cards themselves (which spells costly for apple). Engineers confirmed that there is a powercylcing issue with these cards and said LCD panels that likely is causing the problem.
Trust me - this was the short story. And it sucked.
If you have any specific questions I'd be willing to answer them in this thread.
PS. a little bird told me that this problem is silently acknowledged internally but becuase it's such a small population that it isn't worth the time/money to fix it likely will never be addressed.