Ever wonder how many watts a new microwave should have? Every model boasts its wattage, so it must be important, right? If you are deciding between two models and one has 100 watts more power, should you pick the more powerful one?
Wattage translates directly into cooking power, so more wattage will cook food faster. However, higher wattage models also tend to be the larger capacity models. If you select a model for its larger capacity, you might be planning to cook larger items and so the added wattage just keeps you on par with a smaller model cooking a smaller serving at a lower wattage. On the other hand, small servings will cook faster in high wattage unit than a low wattage unit; so you might select a large capacity unit in order to cook things in less time.
Two models with only 100 watts difference will not cook much differently. The slightly higher wattage doesn't make a large difference in cooking speed. You would be better off choosing the model for the other features that better suit your needs, than opting for more power.