Hi daviddaviddavid,
Having a calm mentality on Test Day can certainly be beneficial. Beyond that though, it's important to remember that you DO have enough time to answer all of the 'gettable' questions - and you should just dump any questions that you think are too hard or too weird. The silliest mistakes that you will ever make on Test Day will occur when you don't take the proper notes... Thankfully, by taking all of those notes (doing work on the PAD and NOT 'in your head'), you'll be amazed how much easier the Test becomes AND how much higher you'll score. The GMAT will always give you the score that you EARN, so go into each question with the will/focus to earn those points.
GMAT assassins aren't born, they're made,
Rich