No prob on the Panamera comparison. I'll make it brief after a long day but can expand more as you wish.
Handling goes to the Panamera. Not that the 6 is bad, but the P-car has ARS, comparatively speaking, built in. However, it is important to order it the right way. There are way to many options in the Panamera and can drive you nuts. I would drive multiple configurations and then decide. Air suspension or not, and others are some questions to answer, for your own liking. Both are quite nice interior. Different. BMW hassle tech. Porsche keeps it simple to use but enough for what we need. The navigation in the dash is very nice! Bose in the P is slightly better than BMW's premium sound. Burmeister blows the whole smorgasbord of car audio out of the park. I went with the middle seats. Not the basic and not sport. Sport was too hard to my liking. The 14 way seats are comfortable. Very. And supportive. Rear seats are awesome despite the deep bucket appearance. Lots of room and very comfortable. The Porshe, being an 8 cyl (I had a Pana S), got excellent MPG. city/hwy mix of 85/15%, for me, and I got about 20-22. 28 on highway. And no, it's not backwards. 85% around town!
The Porsche is extremely refined. It's svelt like, best way to describe. On the one hand, it's a soft, comfy ride and took bumps smoothly with no banging(m sport tires a bit harsh over bumps and road imperfections-sport, sport +, comfort. Comfort + brings it to a well tolerated and unnoticed passing. Corning is where both are about equal. Porsche does it a bit flatter and smoother, BMW does it more sports like. While we would look at the Panamera as a sports car, and it is, it truly drives like butter. The tranny is smooth as silk. I mean silk!
So why didn't I buy another? A few reasons. While it certainly was revisited a hundred times and tops on the list along with the 6, it's a 3 year old body style vs a new look, for me. Outside of the Panamera is ok. It's clean and people Know exactly what it is immediately, but not especially pretty. The 6 is no doubt the current looker.
Both builds are of exacting precision and remarkable engineering feats. I've always been impressed with the underside of my BMW's, and for those cars who had some panels replaced, to see the guta was impressive. I was at a friends body shop that is a very high end Porsche/Audi body shop only and he had about 10 Panameras there. First, for a tiny shop, that's alot of cars. This means that the drivers are enjoying there cars a little too much, perhaps. Lol. But seriously, roaming around I had the chance to see through the front end and rear of a Panamera. Wow. Equally impressive as BMW, but different. Porsche doesn't apparently like hollow space in there bodies and I saw quite a bit of what
Looked like molded styrofoam filling larger pocket. I assumed for noise reduction and other things. The entire undercarriage is covered in high quality components.
I think the reason the Porsche drive smoother and handled roads nicer was the tires. Pirellis. But not 1" thick like the M-sports. Regular looking sidewalks. And Y rated to boot. (Think I got that right). Not runflats. As you may have seen, the F10 board is hellbent on changing out of runflats into regulars. I think that may apply on this car as well. I won't do it but that's probably the key difference, in my experience.
I'm only 5 hours, barely, into the 6 purchase so too soon for me to be picky. But rest assured, I will find the many highlights of the car, and also unfortunately the many issues. So far, the only thing I've noticed is a very light creaking noise when pulling driver interior door handle to close door. Seems a little plasticy (sound wise). Should be easy fix. Otherwise, I'm was more impressed driving it and more satisfied and comfortable then I was during the 3 test drives I did on them today (had choice of 2).
Visibility is slightly worse on the 6 than the Panamera. You will get used to either in no time. Don't let that dissuade you either way unless you need better visibility.
Regarding why I went with the 6 and not an 8, well, that is something I will often regret over the next couple years. But I will say that the 6 impressed me enough that I didn't hesitate to buy it. I would have loved the rumble of the 650, and the nappa vs my Dakota, but as I said, it was a no brainer deal for me. One comment on the 640i Dakota vs nappa- no doubt the nappa is gorgeous. When I looked at both in same color, I realized that the ventilated portion that we sit in, is the same in both. It's the bolsters and backs that have the nappa with visible fillers of Dakota. So when pushed came to shove, there is just a little of the Dakota that stands out (grain vs the smooth nappa). I settled but am very happy with it. Same lux seats. I'm only 5' 6 1/2 (qt my height I need the extra 1/2"), I could use the seat to rise (tilt)just a tad but more in the front of the bottom seat, but it's so damn close to what I need I'll manage. Just looking for a little more support in front of legs. Could just be my body's build.
Either car will be great. Now, $700 is a huge difference and a completely different league of payments and cars. What kind of #'s and deals are you seeing?
Hope this helps! Good luck.
'13 640i Gran Coupe Alpine White/Cinnamon Brown, M-Sport, Driver Assistance, Lux Seating, Premium Sound, Full LED's
'10 Porsche Panamera S
'09 Maserati Quattroporte S
'08 550i Carbon Black/Natural Brown/Anthracite, Sport Pkg, Active Steering, Comfort access, Sport transmission, rear shades, NAV, Sirius, L7, Ipod/USB, PDC, Heated Front Seats.
'08 750i Sapphire Black/Natural Brown
'06 750i Sapphire Black/Natural Brown
'07 550i Sapphire Black/Black
'05 545i Silver Grey/Black