Interesting thread - my Dezl 760 was just recently stolen, so I'm in the market. Per Gamin, the 660 now has "Easy Route Shaping lets you easily change your route to include preferred roads or cities, just by touching the screen"
I have no idea how well (or not) that works. Wonder if you can exclude roads or cities easily, also? +2 on the downgrade to the smaller screen.
Since a GPS is designed from the ground up to find the shortest or fastest route between two points, it doesn't trouble me much that it may vary somewhat from a complete route drawn in mapping software. I either ignore it, or make sure to put in enough waypoints that it has to follow the preferred route. All units are very far from perfect, but they are a convenient source of information - so having low clearance alerts, turn alerts, etc. does help justify the higher cost.