What is the optimum brew pressure?
Many years ago a 9-10 bar brew pressure setting was typical for coffee machines. Now higher brew pressures are commonly used, with brew pressure settings for domestic Italian coffee machines ranging from 10-12 bar.
My best advice is to leave the pressure at the factory setting as the manufacturer will have your machine set for optimum performance. The pressure setting will have no noticeable effect upon the results in your cup so just leave your coffee machine at the factory setting and brew away with confidence.