When I see it typed as S85, I think of it as Model S 85. By that measure, the P85 should be stated as the SP85. Perhaps it would be better if a space was used. S 85 and S P85. Perhaps not everyone thinks this way, but I know some people do -- the people that mention that the X is coming. If the X had a battery of the same size, you have to specify the model to remove ambiguity.
As for the Model 3, I recommend we unofficially call it the Model E. So you could have an E85 or E 85 for example. Tesla can't officially call it that legally, but we can, and almost no one knows how to type three horizontal bars. Eventually, Tesla will need to talk about the Model E and actually say it's name. If this is a problem, I would recommend they officially name it the Epsilon, assuming that doesn't throw up legal problems too (in which case, maybe the Epselon, which is cute, because it has "elon" in it's name). EDIT-- In fact, I like that so much I'm going to recommend it to Tesla.