Pretty much all Model S P cars are less efficient than their corresponding non-P variants. This is due to the larger motors and to some extent the driving style of the owner.
My P90DL had 242 rated miles when new. It now has 235/236 some 20 months later which is about a 3% degradation.
Regarding seasonal efficiency, from what I have seen the HVAC load of heating the battery, seat heaters, defrosters, steering wheel heater and the cabin heaters during colder weather does account for somewhat greater watt hours per mile in the winter. However I have not see this reflected in my Rated Miles calculation.
TeslaFi has a great chart that shows your S's efficiency over various temperature ranges.