Good question. Constant battle, but I have decided on some 'truths' and force myself to believe them whenever I am tempted to over work. Such as:
I do my best work after having a proper break (more creative, better perspectives).
It's impossible to 'finish', therefore prioritisation is the only real option.
Sometimes overworking creates a cascade of work for others...more emails to be replied to etc. I should be mindful of where I focus to make sure I am not churning up low priority issues for other people.
A success can be NOT getting involved/starting something - aim should be to create the minimum fuss to get to an acceptable quality.
Often when I panic about workload, I force myself to go home and time and again cannot remember the next morning what was so pressing.
When the workload is insurmountable, it is better to focus on radical solutions/strategic adjustments etc. I.e. better to look at the whole process and think if it is needed at all etc, and if not, set about influencing/discussing until everyone agrees with you ;)
Etc. But awful feeling when work is interfering with your personal life. Will be reading this thread closely for tips.