After upgrading to Nuendo 7.03 I started experiencing sluggish behavior during editing (more detail below).
The solution for me was to make sure my iPad app Cubase IC Pro was closed while editing on the computer.
I had been battling serious delays with my system recently (which has been surprisingly rock solid for a very long time). Symptoms included:
unresponsive cursor
mutli-second delays when choosing/switching tools/editing
playback starting followed by unresponsive system.
I trashed prefs, reverted to Nuendo 7.02, then 6.5, changed NVIDIA drivers multiple times, etc. My first relief came when I cut off completely from the internet. Voila! My system was snappy as usual. Good but weird. I need my internet connection as I often track using Cubase IC Pro.
Next I reconnected to the internet but closed the Cubase IC Pro app on my iPad, and my problems disappeared! I have waited a few days to post this, to make sure it was indeed the solution, and for me, it was.