Thanks for responding Rafael
through my testing trying to get the system going I had only FCP open with 1 project/sequence
my main thing is the blackmagic card connects to a external screen which the editor uses to do grading and colour correction on
If we turns off the preview device the rendering required is minimal but when he turns it on to check grading he did before he cant view the clips anymore as he just gets the “unrendered” message so he now has to render his timeline again just to be able to check everything on the screen (this second render can take anywhere between 1 to 2 days according to the estimate from FCP)
all the effects handling is set to be done by final cut pro as well
this is also quite a powerful Mac Pro (8 cores with 8GB ram connected to a SAN environment over Fibre) so i would have thought he would have virtually no memory issues