Re: Porsche's navigation system - DVD-based better than CD-b
Not sure how much this helps, since I don't know the Porsche CD system. I have the DVD version, and have had multiple versions of Nav in previous and current vehicles (incl. 2004 Lexus RX version, which I assume is similar to GX). The current Porsche system calculates routes faster, and recalculates much faster if you take a wrong turn. Its voice commands are more straightforward and give you more warning. The screens are similar, small edge to Porsche. The P system lets you do more while moving (more functions locked out for safety with the Lexus). HOWEVER, the lack of touch screen makes entering a destination a MUCH bigger PITA for the P system. Plus, most of the data entry is with the silly rotating knob, and the menu navigation is inconsistent (in some menus, clockwise moves your cursor down or forward, and in others, clockwise moves the cursor up).
Neither system compares favorably to aftermarket systems (Kenwood, Pioneer) that I have owned or used that cost $2500 US or less and which were easier to program, had better screens, and lots of helpful display options, such as a semi-3D, distance-relational view.
If you don't use it much, the P system will be fine.