The AppleCare service gentlemen just left after much trouble shooting regarding getting reliable output from the ATI Radeon HD 5870 card. He hadn’t seen anything like it before and was somewhat bemused at all the combinations we tried to get the thing to reliably work.
He swapped the old card for a direct replacement, however the Mac Pro still does not reliably boot with the mini-displayport -> displayport cable connected to the Dell 27″ screen. (U2711)
Unlike the old card, it seemingly now reliably boots from either DVI or the mini-displayport -> Apple Dual DVI adaptor. I can then plug in the 27″ after booting, however it’s not really a usable solution having to crawl under the desk and reconnect cables every time I turn on the computer.
So it would appear it’s an issue with the cable. I find it weird that a cable is able to render the entire GPU vanished from the machine, but that seems to be what’s happening. I can’t connect the 27″ any other way and still get full resolution so it loks like another cable is in order.
An Apple forum poster and the NEC document both suggest a male mini-displayport to female display port adapter, then use the displayport to displayport cable that shipped with the monitor. The adaptor is available at monoprice for $5. Shipping is over $30 dollars. Not a great solution.
Macfixit.com.au appears to have what is an identical product (without the monoprice logo) for a little cheaper ($17 cheaper and hopefully faster delivery). I’ll order one of these and see if it does indeed fix the problem. I’ll post another update once I’ve tried this combination.