jb,
It is likely you drove a newer P85 and are comparing it to your current production P+. Although my opinion on this subject is constantly evolving, here is what I think you are feeling.
The primary issue I had with my Feb. delivery P85 was what I can best describe is a "windup" feeling in the rear of the car. Under hard acceleration, the rear wheels would "pull forward", loose traction, snap back and then repeat as the car launched. I also felt this uncertainty accelerating in corners without the slip recovery of course. This was all gone with July P+. It was also gone with my wife's Sept. S85! I came to learn that Tesla was using the stiffer lower a-arm bushings first in the P+ then in all production. As a result, my wife's S85 on coil springs felt REALLY good. Sure, it was as high as a pickup (just kidding here but its up there) but there was a nice immediacy about the feel that reminded me of BMWs. I too am a long time BMW guy and big time M5 fan (or at least up the the V10s).
Given that all production is getting the new lower a-arms, what you get with the production P+ is wider rims/tires, larger sway bars and stiffer dampers. You can do a lot of experimentation of wheels and tires for what 21s cost. As for the larger sway bars, I really did not take issue with roll control on my Sept. P85 and thus did not/do not require the larger bars. With those larger bars comes increased head snatch going over road imperfections or speed bumps at an angle. The increased bump and rebound on the dampers is nice.
At the same time, the P+ insists you have air suspension and I think this is what you are finding less than desirable. Drive an AMG E63 and C63 back to back and you will understand immediately just how different air and coil suspensions are. Some prefer the way air shaves off the sharp edge and feedback of the coils. Others do not. If you are one of the ones that does not (like me), air can be distasteful.
jcaspar,
Yes, it did actually come down to swapping out the coil dampers for air dampers if you start with coil. The air dampers have increase bump and rebound damping over the coils so you get an overall stiffening affect. Bilstein sets ride height using a C clip that locates the lower spring perch. The damper body ID and OD are the same all the way down and Bilstein actually provides truck dampers with multiple grooves for adjustable lift so it is common and accepted practice to have multiple ride height grooves without affecting the structural integrity of the dampers. I simply added some extra grooves to achieve my desired ride height. I started off using 2.5" springs over adjustable spring perches to get me in the ball park for ride height then transferred this knowledge over to an initial guess for added spring clip grooves and stock springs. I was able to confirm that the stock spring rates were going to work for me by trying different rates in 2.5" ID springs. I'm still working through the final ride height (which involves removing the dampers each time to move the spring perch location clips - PITA) but I am getting very close.
WRT the quality and type of dampers, I have never been one to do much damper adjustment. I find something that works for me and then never touch the adjusters. Tesla uses excellent quality Bilstein dampers on MS so, for me, it was a matter of seeing if Tesla already was making something that worked for me. Now that I have my P+ dampers off the car I will put them on the shock dyno and plot bump and rebound against the coil spring and standard air dampers at which point we will know everything that is available from Tesla at this point.
jb, in closing, you should probably stop by and drive my car if you find yourself in the West Palm Beach area
I've found that air dampers on coil springs at Standard air ride heights produces a nice car to drive. It is still not a M5 in outright stiffness but that is ok for me. The feel is much more to my liking now and I am ok without the harsh extreme.
