I would get the nav. For me, it is a no-brainer. I have had integrated nav in my cars for the past 11 years. I could not imagine driving any other way. With a Garmin or TomTom, you have to go the extra mile to setup it up on the dash and it doesn't look good. In regular use, they are not significantly superior to an integrated nav system. But, integrated nav systems are so much more convenient because they are always there for you.

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SOLD
2000 E38 750iL Highline Edition, Upgraded with the lastest 2006 X5 Electronics
MKIV Navigation, 16:9 Display, Bluetooth, TV/Video with Backup Camera, Sirius, and Aux Input