Yes, I have pretty good idea what should fit okay with my suspension and fenders..
Indeed 16" tires are as lowprofile harder to find, only common sizes are probably 225/50/16 and 205/50/16, smallest rear tire size on 993 is 245/45/16, which is not so common anymore..
Yeah, 17" should be okay, quite easy to find low profile tires between 205-275. I think 45 and 40 series tires are lowprofile enough.
Porsche (or any) 17" wheels should be lighter than 18" wheels, but 993 turbo hollowspoke 18" wheels what i have been looking, are as light or lighter than most Porsche 17" wheels..and 3-piece wheels seem to be heavy, except kerscher KRS 3-piece.
Here is some weight data:
http://www.944racing.de/felgengewichte.php
http://forums.rennlist.com/rennforum...ke-wheels.html
This finnish 1303 has 225/40R18 and 265/35R18 tires, looks quite wide, rear wheels look like 10" wide: