I wonder if the 3.9s is a safe value achiveble by both AWD with 990 and 980, (so the marketing works) but that in real life 980 motor will do better than advertised (and get to 3.5s like the P3D).
The front motor is the main limitation on the AWD, not the rear.
I am hopeful the upgrade is the 20% rumored here (more hopeful for full P but seems unlikely).
A 20% improvement over the published 4.4s 0-60mph gets you to 3.5s, which just happens to be the 0-60s time I found in the source code of the design page. With 1-foot rollout that should be in the low 3s and a clear buy at $2k.
Tougher putt to only pick up 0.5s for that amount.