5-sp is the 750
4-sp is 442 (on the diesel)
The problem with the navi is that it also controls the ventilation (hvac). So, if it fails, it's a required expensive repair/replacement. And you cannot chose to have a better navi or, even worse, a better sound system, without it beeing an add-on.
BTW, as far as I understand, it's easier to connect your ipod to the navi-radio than to the standard sound system in the non-navi.