This is a good test of 15", 16", 17", 18", and 19" wheels/tires. Bottom line: larger wheels yield small improvements in cornering grip at the expense of reduced acceleration, fuel economy, and ride comfort. However, larger wheels look better.
At the end of the day, you can justify whatever you want.
Effects of Upsized Wheels and Tires Tested - Tech Dept. - Car and Driver