Playback issue with 2k Prores 4444 after update of OS and FCP.

Hi,

This is going to be a strange query so hang in there with me.

I am cutting a full length feature shot on the Alexa working directly with the 2k Prores 4444 source footage on my Mac Pro in FCP7. This is the SECOND film I have cut using this workflow and therefore know it is tested on the platforms I use.

My mac is rarely updated (I KNOW!) as I really do use it solely for editing and therefore do not have it connected to the internet ever. I did update it over the weekend and now am having endless difficulties with playback. This playback issues have never been present before and therefore lead me to believe that it must have something to do with the new updates. I'm not even sure what updates I actually installed as I said yes to all, and then again, and again...

Before I was on OS 10.6.3 / now 10.6.8

FCP was not updated as I'm still using 7.0.3

Info in FCP:

I use the LUT plugin from Antler to convert from LogC. I also use top/bottom slugs to view my screen as 2:35 and get rid of unslightly booms etc.

There is therefor a fair amount of rendering that needs done as I work. It's a pain, I know! HOWEVER before doing said updates I never needed to render in order to see a full preview without any droppped frames and was even happy to view with Director/Producer using unlimited RT (orange render bar). Now EVEN if I am fully rendered my machine is stumbling and spitting the playback. Obviously I can not work this way.

The previous feature and this one are stored in the same manner. I use an external RAID connected using eSATA. Renders are all to the same internal drives.

please let me know if anyone has encountered a similar issue and whether I need to go back to a previous/newer OS.