First of all, welcome!
640i hands down on looks.
Panamera hands down for driving (assuming you're looking at the V8).
I don't think I could go for the 640i instead of paying slightly more for the 650i - my first choice for this type of car. A 640i is about $95,000 well equipped, so $102k to $105k is a small % for such an important upgrade. If you don't want to do the 650i, then I think I'd do the Panamera. It definitely gets unique points in the sea of BMWs. Between the Panamera and the 640i, I'd take the slightly odd rear styling of the Panamera (just my opinion) over the 6 cylinder 640i. The fact that BMW can get away with charging nearly $100k for a huge car with 6 cylinders is really quite astonishing. The 6er really is beautiful inside and out, so I guess it helps
