Derek,
I think that it's very difficult to judge the efficiency of the filters just by their appearance, but Porsche will have conducted a significant amount of development work before coming to the conclusion that the filters only need to be changed after 60,000 miles.
I would think that 20k miles is a sensible time to think about changing them, but at the end of the day it's just a personal choice and it can't do any harm.
Jeff
I think that it's very difficult to judge the efficiency of the filters just by their appearance, but Porsche will have conducted a significant amount of development work before coming to the conclusion that the filters only need to be changed after 60,000 miles.
I would think that 20k miles is a sensible time to think about changing them, but at the end of the day it's just a personal choice and it can't do any harm.
Jeff