OK the system Windows-performance rating issue was due to powersaving option.
BUT I have just tested: Only video and one audio file in N5.5 stutters badly. Same setup, same video and audio track in N4 runs smooth as butter.
So somehow the N5.5 video engine has been screwed or doesn’t behave like it used to. Any ideas what could be causing this? Desperate for a solution before the next Nuendo job comes up!
Cheers,
Andrew