Actual measurements on my 2001 non-S model (taken in inches, converted):
Rear edge to bottom of logo: 50.8 mm (2")
Sides to R/L edges of logo: 279.4 mm (11"). Of course, ending up centered.
I was surprised to see the measurements come out in whole inches, I expected some crazy fractions due to originally being in metric units. I now wonder if Porsche's CAD system or stylists are using US/English units?