If your looking to keep your car running at optimal officiency, and your driving a manual transmission, shifting at 3k (the three on the tach) is the best bet. It doesnt tax the car by any means and will result in good gas millage and engine longevity. If your going to be doing any kind of spirited driving shifting before the tach changes to red is required to prevent serius engine damage. Most engines however have revlimiters to help prevent damage of this kind. I would avoid driving your car to hard untill you know more assuredly how your engine runs under different situations.