I have a 550i 6-speed. I had a very hard time driving it smoothly at first. I think the culprit is the CDV (clutch delay valve) which my prior car (E90 M3) didn't have. After about 5,000 miles, I'm much better at it now. IIRC, my 540i/6 and 335i had CDVs; my two M cars didn't.
After driving the high-strung M3, I'm LOVING the low-end torque of the 550i. It's a few ticks slower than the M3 to 60 mph/100 kph, but the acceleration at highway speeds is stunning. When I want to move into the passing lane (let's say, accelerating from 45 or 50 behind someone who doesn't know how to merge) up to ... oh ... the legal speed limit
, the acceleration is stunning. In these situations, I go from sixth to third and floor it. The torque and the adrenalin are incredible.
I remember reading a review some time ago -- I *think* it was for the E39 M5 -- that described the car as being an "alchemy chamber for converting dead dinosaurs into adrenaline". This car clearly qualifies for that description!