Went from an early 2013 P85+ to a late 2014 P85D, and then to a late 2016 P100D.
1. After driving P's, it would be difficult to go back. Yes, a 90D and a 100D are quicker than most other cars on the road, and certainly "fast enough" for any sane use case. I don't drag race, I don't go WOT at every light, etc. But on occasion it's rather fun to take an on-ramp, and I like the immediate passing capability >65-70mph. The non-P's give up much of their acceleration above 65. I took out a 90D before I bought the P100D and I just couldn't do it. ymmv.
2. I wanted AP2, and keeping non-metered supercharging was desirable, but not a show stopper (real $ benefit to this is not as much as one might think, unless you're towing with an X all the time).
3. Got a discount on a showroom car in Q4 that put me over.
I'm now ~5-6 weeks post purchase:
1. I really miss the + suspension and sway bars from my early P85D. It also turns out the steering is different. Apparently Tesla changed suppliers and I can feel the difference. It's less precise and I can't feel the road as much.
2. I miss the HID headlights. Sadly, the LEDs are not as good, and they should be better.
3. I'm concerned about the latest safety ratings. I hope Tesla redesigns the headlights and offers an at-cost upgrade, and fixes the seat belt issue free of charge.
4. The range can't be beat. A P85D is really closer to 80kWh, whereas the 100 is 98kWh (usable). I get 316 rated miles @ 100%. I charge to 80% daily, so theoretically my degradation should be less.
5. Superchargering on the 100 is quite nice. In 45-50F temps today I was still at 115kW at 170 rated miles, and 46kW at 290.
The 100D is by far a better value. If you make the decision with the left side of your brain and your wallet you'll get the 100D. If you're making it with the right side of your brain you'll get the P100D.