Tuan,
As long as the wheels have the correct width, bolt pattern, and offset you can slap them right on. I went from 17's to 19's and love the look. Many think they look out-of-place on a Boxster.
Generally, the bigger wheels and tires are heavier than their smaller counterparts and you can definitely feel a difference in performance. It just takes more energy to get the bigger, heavier wheels and tires turning so the car feels more sluggish off the line.
I didn't notice much more road noise but they generally ride rougher due to the smaller, stiffer sidewalls. The larger tires are more expensive too.
ddb
