Hello,
i had Michelin Pilot Sport PS2 with N and without N. The N is a little bit more precise – especially steering – if you drive the car very hard. The non N is over all more comfortable. Seems that the Michelin N tyre has a stiffer tyre flank.
But the car will drive with all tyres. I think there is no need to have N tyres.
Porsche has a list of tyre recommendations for summer and winter tyres for the 986/996:
Summer:
http://files.porsche.com/filestore/download/germany/none/classic-galleryanddownloads-tyreapproval-summertyres/default/555ddd04-f0d2-11e5-84b6-0019999cd470/%c3%9cberblick-Sommerreifen-Classic-Fahrzeuge-und-Youngtimer.pdf
Winter:
http://files.porsche.com/filestore/download/germany/none/classic-galleryanddownloads-tyreapproval-wintertyres986-996/default/a2fd233a-f299-4d68-a996-22920691dfe7/%c3%9cberblick-Winterreifen-996-986.pdf
Don't know if these tyres are available in the US, but maybe in Sweden. In general tyres in Germany / Europe are different to the tyres in the US / Canada / ROW.
Regards, Markus