Here's a site which lists weights for a lot of the Porsche wheels and also includes offets, widths, part numbers, and pictures for a lot of the OEM Porsche wheels:
944racing
My favorite 17" wheel is the "Boxster S" twist, I have a dinged up set of those as my track wheels. I have a set of "996 Carrera 2" in 17" as my street wheels that I repainted using the guidance from some of the threads in the DIY section. They look pretty good from 5 feet away, as you get closer you can set a spot here or there.
There are plenty of 18s that will work on the Boxster without spacers and fiddling that can get you away from the twist look, and also some 17s.
Good luck!
Steve