Check this site out for some weight info on the Porsche wheels.
A couple of our wheels also come in 17x9 ET55 for the 996, with a small spaces some folks run them on the back and run the 17x8.5 ET50 on front, also with a small spacer. I know a guy that runs this setup (with the same wheel you're looking at) and runs 275/40/17 in back with 255/40/17 up front.
944racing