Don't try and drive anywhere in Yorkshire in a 5-series. You may end up on the edge of a cliff.
I don't have a sat-nav, but I used a widescreen Garmin nuvi in the States (the one that Avis hire out at a lucrative rate) and found it to be very good. The larger screen size compared to the budget TomTom models (not actually driven with one of those, but been in a car with a friend who was using it) is pretty nice, and the mapping is nice and clear. They rent out the models higher in the range, but the basic features (i.e. what I liked) are the same as one I saw for about £97 in Tesco yesterday.
There's my limited experience... all 1300 miles or so of it.
Have you ever felt like you could float into the sky / like the laws of physics simply don't apply?