P85DL+, with Recaro rear seats, wow. The only thing that would up your unicorn-ness would be gray or black Arachnids, as they no longer offer them for redemption as a referral prize. Just silver is offered these days. I've seen a few gray sets (I have 'em in gray) but I've only seen 1 black set personally.
/edit, although, now that I think about it, the only time Recaro rears were even potentially offered was during that brief "+" era. The two went hand in hand even though not everyone got them.
/edit 2. Another potential unicorn addition would be executive rear seats in a P85DL+...