What is the difference between the performance plus suspension vs. regular smart air suspension on those P85D?
The P+ suspension is the same suspension on the p85+. More firm for aggressive driving. Most (if not all) P85Ds built before April 2015 have the + suspension, after April they commonized the suspension on all model S vehicles.
Here’s a couple good reads.
P85D (pre/post April) ride performance
Performance Plus (P85+) vs. Performance (P85) Test Drive and Review