Hi Nicholas.
Did you ever fix the issue? I have had the exact same issue as you and been through various rounds of re-installing and stress testing at Apple in the US.
It has been a complete nightmare and I’ve kind of resigned myself to waiting until the new FCS comes out in June.
Through all the testing by myself, Apple and Tech Serve I’ve come to the conclusion that it’s a software issue with Final Cut. I heard that it may have something to do with the 12 cores and that Final Cut doesn’t recognize that? (My details are vague on that point so feel free for someone to correct me).
My setup is two 27″ ACD’s, 2 x 2.93 6-core Xeon Processors, 24 GB RAM and two Radeon HD 5770 graphics cards.
If anyone has any more info on this or Nicholas, if you managed to find out a way to work with it, let me know. Until then I’m just trying to “apple-s” my way to June.