n4ally2, I briefly drove a Cayman S this summer with those tires on 19" wheels, and thought they were excellent. I did the clover-leaf on route 53 and Paletine Road about 24 times as the test track!
Are you sure they are the "Porsche N0" version? I did not see that on your link. Tire Rack sells this tire (N0 version) for $275 each (rears).... a few dollars less than your price. Granted, the road hazard warranty was more. So net/net you received a better total price.
Who will do the install?
Make sure you take photos (with the daily newspaper) to document your wheel condition prior to the tires being mounted, to protect yourself if the wheels are damaged during the process.