We have a late 2012 S P85.
I agree the OP made the right decision in going for the P85 over the 85.
Unlike the new P cars, the P85 has the same range as an 85, and comes with the faster acceleration (0-60 in 4.2 seconds), which is the same acceleration as our new S 100D. While that acceleration is faster than what is needed for normal driving, it's comforting to know that it's there, just in case you ever need it.
The other feature differences between the early production P85 and 85 models - you get the spoiler plus there were some interior upgrades - (seats and liner?).
One warning though... The on board Trip Planner has not been as reliable in predicting charging levels and needs with a P85 compared to our new S 100D. With our S 100D, the Trip Planner does a pretty good job in estimating charge at destination, and, if anything, is too conservative in estimating how much charge is needed before leaving a supercharger.
With our S P85, we had the opposite experience. The Trip Planner was way, way, too optimistic - consistently overestimating the predicted charge at destination, and often when we used the Trip Planner estimates, we'd have to slow down considerably between chargers, just to stretch the charge far enough to make it. Which means that we'd end up staying at each supercharger longer than recommended, to ensure we'd have enough charge to make it to the new charger - and maintain full highway speeds.
For our S P85, we used a "30-30" rule to estimate how much charge we should have before leaving a charger. We'd take the distance to the next charger or destination, add 30%, and then add an additional 30 miles of buffer. For example, if the next charger is 100 miles, we wouldn't leave the current charger until we had at least 160 miles of rated range, no matter what the Trip Planner was telling us. And using that rule reduced the number of times we had to slow down between chargers.
Our new S 100D, is much more energy efficient (likely due to the dual motors) - and we've found the Trip Planner is relatively accurate.