Hey Sean, the official stable QT for FCP 4.5/OS10.3.8 was 6.5.2.
I’m running QT 7.0.1 and a FCP 5 system with a Kona SD and the beta BM drivers, everything has held together *very* well so far. BM has really done us a favor by supporting the Kona SD (which is a very good card, honestly). I really thought it was going to be another Digital Voodoo (talk about being left out in the cold with some vaporware). Because of that support, I’ve bought Decklink cards for our last two systems.