I got rid of my 2013 550 M-sport for the 85D. I vboxed both of them. The 85D is over 1 second faster to 60mph, 100mph, and in the quarter mile. And that's not taking in to account "real life driving" where the 85D doesn't have 8 gears worth of downshifting to deal with when you want to go...it just...goes. Like you, I was also unwilling to drive anything slower than my 550, which to me, was already borderline at 5.0 0-60. Most other cars I've owned were in the low 4's. The P85D is awesome, but if you just want something faster than your 550, the 85D is the best bang for your buck. If you're looking for a more direct acceleration comparison, the 85D is slightly faster 0-60 than the 2016 M3 and 2016 C63 AMG, and identical in the quarter mile (albeit at a slower trap speed).
Don't be put off by Tesla's website that tries to tell you the 85D is 0-60 in 4.4. It's really 4.0 if you use the standard 1-foot rollout method that all the magazines and other car manufacturers use to compare 0-60 times. I frankly think it's dishonest that they show the P85D with a rollout, and the 85D without, just to make the P model look better by comparison.
The only things I miss from the 550 are the soft closing doors, ventilated seats, and butt massgers
. Everything else about the 85D is better. You'll also be surprised that while the 85D is 1,000lbs heavier than your 550, it feels like it weighs less. It's the size of a 7 series and feels like a 3 series. Pretty remarkable what putting all of the weight in the floor can do
.
Also, just to be clear (and I think we're already on the same page here): Like the 550, the Model S is not a nimble sports car. It's a very quick luxury sedan, with almost rocket ship-like acceleration. I can say from experience that it does handle better than the 550. But if you want a car that is truly sporty and nimble, you'll want a real sports car that's light weight and meant for canyon carving and the occasional track day. If you want a car that comfortably seats 5, has instant torque, and can basically drive itself...get the Tesla.