My take is this:
The 535i feels pretty damn beastly to me, so I purposefully don't want to drive a 550i as the Herculean effect of my car will wane.
I actually didn't consider a 550i, and I found some pretty good deals on CPO ones. Reason being further than just budget. I've been fawning over the N55 ever since it made its initiation as the N54. IMO there's something about the BMW I6 experience that you just can't match elsewhere. The sound, the unique feel, I just wanted my BMW with the infamous buttery smooth and BMW-blooded I6. Now, that said, this I6 isn't like the wind-it-up I6's of yore, so to purists it might feel too altered anyway, but to me, it brings a torquey V8 feel that now gave me the best of two worlds: Characteristically BMW I6 with a V8 feel around town.
On top of that, of course the F10 is a heavy beast on its own that isn't exactly a "drivers car" in that purist sense, but numerous Reviews state how the 550i feels less balanced than the 535i, more noticeably front heavy (if I'm not mistaken, it doesn't uphold the "BMW Perfect 50/50 weight distribution"?), less nimble, not as dialed in on the handling side, etc.
To top it off, as one of the Rags said in a review, the N55 is like the perfect child, it does everything right. Smooth, small but feels big, sounds great and unique, gets GREAT MPG WHILE having an exceptionally low and flat torque band, and can clock a 1/4 mile in just under or around 14 seconds at around or over 100 MPH. All things considered, the way it puts that power to the ground (low end heavy and geared so well so IMO it feels faster than it is around town), this heavy car its in, the MPG, the balanced weight distribution, it's quite impressive.
Now, all that said, as much a rush as I get from the effortless power, instantaneous torque, very eager throttle-and-go in Sport mode with my SAT in this 535i, I know if I drove a 550i it'd just blow my socks off, and I'm sure I'd be clamoring for more.
Another note: The 535i puts about 280 HP to the wheels before being well broken in, which would put it realistically at about 335-340 HP at the crank with about 343-345 TQ (283-285 RWTQ). The 550i seems to clock a 1/4 mile at about .8-1 second and 8-10 MPH faster than the 535i, and considering it weighs considerably more, it would be safe to assume it is equally underrated.
'13 F10 BMW 535i Sport
: Jet Black/Black-Anthracite : Premium & Technology Packages/Sport Auto Trans/Camera/Park Distance Control/Heated Seats/Tinted Windows/Blacked Out Markers/Performance Spoiler.
Ex M-B's: '11/'10/'06 E350's w/ AMG Sport Package, '02 S500 w/ Every Option.
Last edited by K-A; 01-19-2013 at 06:18 AM.