That dropping frames bug is absolutely not GT120 related.
It’s blackmagic driver/10.8/ FCP7 related
Even with ATI 5770 / ATI 5870 cards this bug is there.
10.8 , Blackmagic 9.7 video driver and FCP7 is a no go on pretty much any system.
You get dropped frames with just a color bar in your sequence.
When you disable the audio playback, the dropped frames is gone.
We have reproduced this on many systems.
Blackmagic is aware but are not sure if they can fix it, as it’s only a problem in FCP7.