19" wheels just look really weird to me on the 986. they make the car look smaller and rubber band tires make the wheels look bigger. The Cayman and 987 seem to pull off the 19"s a bit better.
The Boxster is a performance driven roadster, meaning its engineered for aggresive cornering. You need some rubber on the car and the wheels should be light, closer to 20 pounds than over 30. Heavy wheels on low profile rubber will cause to much cowl shake on a convertible. That leads to things coming loose, rattling and stress all around. The other thing is that at 19" you will have fewer tire choices.
I've always like the two piece speedline wheels that most ressemble the original Boxster concept car. They're often seen on the 968 too.
speedline wheels